Full text of "Animal life in deserts, a study of the fauna in relation to the environment"

ANIMAL LIFE IN DESERTS

ANIMAL LIFE IN
DESERTS

A STUDY OF THE FAUNA IN
RELATION TO THE ENVIRONMENT

P. A. BUXTON, M.A.

FORMERLY FELLOW OF TRINITY COLLEGE, CAMBRIDGE
MEDICAL ENTOMOLOGIST, GOVERNMENT OF PALESTINE

ILLUSTRATED

LONDON

EDWARD ARNOLD & CO.

1923

\^All fights reserved]

\\io

B^8

Made and Printed in Great Britain by
Buder & Tanner, Frame and London

PREFACE

Circumstances over which I had no control
induced me to study the conditions of Ufe in Lower
Mesopotamia and in North- West Persia for more
than two years. I had previously seen desert life
in spring-time during a short visit to Algeria, and
more recently I have lived in Jerusalem, a city
which is not indeed in the desert, but within easy
reach of the deserts of Southern Palestine and of the
lower end of the Jordan depression. I have endeav-
oured to summarize my own observations and to
elucidate their meaning by comparison with what
has been observed in other deserts. The desert is an
environment unspoilt by the hand of man, so that
one can more clearly observe the interaction of
plant and animal upon each other, and the depen-
dence of the living creatures upon climate and
other physical conditions.

This " oecological " study will, I hope, prove
interesting to many who delight in natural history,
but who have never had an opportunity to make
themselves acquainted with the more formal aspects
of Zoology. As every reader will discover, the study
of the animal in relation to its surroundings is beset
with difficulties ; we are ignorant of certain details

vi PREFACE

of the climatology of deserts, and of the life-history
of the great majority of the smaller animals, and
there is at present a complete absence of experi-
mental work upon them. It is partly in order to
summarize our present knowledge and to draw
attention to the graver deficiencies in it that this
book has been written.

The study of the desert creatures and their
environment leads one to a very fascinating meet-
ing-place of several sciences. It can only be
approached with the help of botanists, meteorol-
ogists, physicists, and others. My debt to my
fellow-workers is the greater because the book was
written in Jerusalem, without access to a good
library ; I have therefore been forced to rely on the
kindness and generosity of correspondents, many
of them unknown to me personally. In many cases
I have embodied the information which they have
given me, and made no acknowledgment of it in
the text, because my purpose has been to eliminate
foot-notes and bibliography from a book which can
make no claim to completeness.

My friends Mr. C. B. Williams and Mr. V. H. W.
Dowson have allowed me to draw upon them for
several illustrations. Fig. 11 is from a photograph
taken by Mr. F. W. Green, and to him and to the
Director of the Geological Survey of Egypt I wish
to express my gratitude. For Fig. 32 we are in-
debted to Dr. R. I. Pocock and the Zoological Society
of London ; for Fig. 34 to Mr. E. C. Stuart Baker
and the Bombay Natural History Society ; for Figs.
38 and 41 to Dr. J. Grinnell and the Museum of

PREFACE vii

Vertebrate Zoology, University of California, U.S.A.
I am indebted to the Director of Agriculture, Iraq,
for the data on which Fig. 8 is based : I am also
extremely grateful to Miss A. M. Gayton and Mr.
Engel Terzi for the line drawings. My friends
Mr. C. B. Williams and Mr. W. E. Evans gave
me invaluable assistance in the preparation of
Chapter I (" The Desert Climate ") and Chapter III
(" The Floral Environment "). To my wife, my
sister, and my mother my best thanks are due for
help in preparing the book for the press.

P. A. BUXTON.

Jerusalem.

June, 1923.

CONTENTS

CHAP. PAGE

Pbefacb V

I The Desert Climate 1

II The Soil and Watercourses .... 36

III The Floral Environment 63

IV Animals and the Physical Environment . 64
^ V Animals and the Physical Environment (contd.) 81

VI Relations between Animals and Plants . . 122

VII Colours of Desert Animals . . . . 140

LIST OF ILLUSTRATIONS

FIG.

1. Graph showing the Average Monthly Rainfall of five

Places in the Great Palaearctic Desert . . p. 7

2. Graph showing the Average Monthly Rainfall of five

Places in the Indian Desert . . . . p. 8

3. Graph showing the Average Monthly Rainfall of four

Places in the Deserts of the Southern States of the
U.S.A. The distribution of rainfall shown in this
graph is not characteristic of stations in every part of
these deserts . . . . . . . p. 9

4. Graph showing the Average Monthly Mean Shade

Temperatures of three Places in the Great Palsearctic
Desert p. 16

5. Graph showing the Monthly Mean Maximum and Mean

Minimum Shade Temperatures of four Places in the
Great Palaearctic Desert . . . . p. 18

6. Graph showing the Monthly Mean Maximum and Mean

Minimum Shade Temperatures of three Places sit-
uated on the Sea Coast of the Great Palaearctic
Desert p. 21

7. Curve obtained from Recording Instrument showing

daily Fluctuation in Relative Humidity at Gizeh,
Egypt, 20th-22nd March, 1922. The figures on the
side of the graph represent percentages of humidity
(C. B. Williams) p. 24

8. Graph showing the Relative Humidity at Mosul, N.

Mesopotamia, at 8 a.m. and 4 p.m. during an average
Week in June and an average Week in December p. 25

9. Graph showing the Mean Relative Humidity at Two-

hourly Intervals for the Months June, July, August,
and September at Mohammerah, Persian Mesopo-
tamia p. 26

xii LIST OF ILLUSTRATIONS

FIG.

10. Artificial Depressions in Sand Dunes at El Wad, S.

Algeria, planted with Date Palms which are drawing
on Subsoil Water. The sharp margin of the oasis and
the utterly barren nature of the dunes are apparent.
{Photo : V. H. W. Dowson, July, 1922) facing p, 42

11. Ridge of Cretaceous Limestone hollowed and carved by

Wind-driven Sand, at Umm Shersher, S. of Kliarga
Oasis, Libya. (Photo : F. W. Green, Greol. Survey
of Egypt) facing p, 42

12. Date Palm growing in a Pit at El Wad, S. Algeria. The

contrast between the flourishing palm which has
tapped the subsoil water and the utter absence of any
undergrowth is striking. The palm-leaves inserted in
the sand in the foreground are intended to check
drifting sand. (Photo : V. H. W. Dowson, July,
1922) facing p. 44

13. Bare Expanse of Salt Mud at the North End of the Dead

Sea, Palestine, with two or three tufts of salt-loving
bushes : within the historical era this area was
beneath the waters of the Dead Sea. (P. A. Bux-
ton, photo) facing p. 44

14. Salt Patch in Lower Mesopotamia. The white area is

covered with crystals of salt ; the darker margin lies
a few inches higher, and is therefore slightly less salt :
the few small bushes are Suseda. (V. H. W. Dow-
son, photo) ..... facing p. 46

15. Salt-loving Vegetation (Atriplex halimus, etc.) on

the Plain of Jericho, Palestine. (P. A. Buxton,
photo) ...... facing p. 46

16 & 17. Hills near the Mouth of R. Jordan, near Jericho,
Palestine. These hills contain such a high propor-
tion of salts that they are almost entirely bare of
vegetation. (P. A. Buxton, photo) . facing p. 48

18. Wadi Nar, S.E. Palestine. This is typical of a certain
type of rock desert, in which the strata of bare rock
alternate with softer material ; it is full of crevices
and on it grow a large number of spring flowers, and
it contains caves (pages 104-105). Typical birds are
Rock Doves, Black and White Wheatears (Saxicola
lugens)^ Rock Partridge (Alectoris), Ravens (Gorvus
ruficeUis), and Tristram's Grackle (Amydrus tris-

LIST OF ILLUSTRATIONS xiii

FIG.

trami) ; among mammals, the Coney or Hyrax
{Procavia). (P. A. Buxton, photo) , facing p. 50

19. Sandy Bed of a " Wadi " near Gaza, Palestine. For a

few days at a time this bed will flow rapidly :
though subsoil water is available at no great depth
no bushes grow in the bed of the wadi because of
the winter floods. (P. A. Buxton, photo) facing p. 50

20. Wide Bed of a Flood Channel near Jericho, dry except

for a few days or even hours in the year, but bearing
a rich flora of perennials because of the presence of
subsoil water. (P. A. Buxton, photo) . facing p. 52

21. Bed of a Wadi at Biskra in the Algerian Sahara,

showing Bushes of Oleander (Nerium) and Tamarisk
(Tamarix). (V. H. W. Dowson, photo) facing p. 52

22. Wilderness of Judaea, between Jerusalem and Jericho.

These chalky hills are covered with annual vegetation
in March and April and for the rest of the year are
bare, except for very inconspicuous perennials

facing p, 54

23. Wadi Kelt, Wilderness of Judaea, Palestine. On the

left of the picture are various trees and bushes, wild
and cultivated, owing their existence to the perennial
water of the wadi ; they are in no sense in the desert.
On the right, a couple of yards from the sharp edge
of the oasis, is the barren wilderness, at this season
(July) showing nothing but withered annuals and
a few small bushes of perennials. For a general
view of this country, see Fig. 22. (P. A. Buxton,
photo) ...... facing p. 54

24 & 25. Photographs taken within a few hundred yards
of one another in February (Fig. 24) and June (Fig.
25). The spaniel dog gives an idea of the depth of
the annuals in spring and of their closeness to each
other : in summer the earth is bare and the perennial
Zizyphus bush is the only conspicuous plant. (P. A.
Buxton, photo) .... facing p, 58

26. Stony Hill-side on the Mount of Temptation, near

Jericho, Palestine, showing spring vegetation (Feb-
ruary) and in particular the broad tufted leaves
of the Mediterranean Squill (Urginea). (P. A.
Buxton, photo) .... facing p. 60

27. Cahtropis procera (Asclepiadaceae), in the Plain of

xiv LIST OF ILLUSTRATIONS

FIG.

Jericho, Palestine. This bush belongs to the third
group of desert plants, the perennials which exist
above ground at all seasons ; the leaves are succulent
and contain great quantities of a bitter, milky sap.
Fragments of dead annuals may be seen. (P. A.
Buxton, photOj October, 1922) . . facing p. 60

28. Graph showing the Number of Species of certain

Families of Orthoptera present month by month in
Collections made at Amara, Lower Mesopotamia,
by W. E. Evans and the Author . . p. 66

29. Graph similar to Fig. 28, showing the Monthly Prev-

alence of the Fossors (" Solitary Wasps "), Bees,
and " four families " of Hymenoptera (i.e. Fossors,
True Wasps, Bees, and Ruby Wasps) at Amara p. 67

30. Graph similar to Fig. 28, showing the Monthly Prev-

alence of Pyrale and of Noctuid Moths and of all
Families of Moths except Pterophorina, Tortricina,
and Tineina p. 68

31. Hairy-footed Jerboa (Jaculus jaculus) from Egypt.

Notice the long hind-legs with reduced number of
toes, and the long tail with a terminal tuft of hair,
and the biped attitude. (Drawn from life by Miss
A. M. Gayton) p. 75

32. Under-surface of Right Hind-foot of Allactaga indica

(A), Scarturus tetradactylua (B), and Jacultts jaculus

(C). (After R. I. Pocock) .... p. 76

33. East African Gerbil (Taterona vicina) from East

Africa. This animal is typical of a very large
number of species, most of which are found in
various parts of the Great Palsearctic Desert.
(Drawn from life by Miss A. M. Gayton) . p. 77

34. Imperial Sandgrouse (Pterocles arenarius). (After E. C.

Stuart Baker) .... facing p. 84

36. Addax Antelope (Addax masomaculatus), Male, from the

Sudan. (Drawn from life by Miss A. M. Gayton) p. 90

36. Arabian Oryx (Oryx leucoryx), an Inhabitant of Water-

less Sandy Desert. (Drawn from life by Miss A. M.
Gayton) p. 91

37. Persian Gazelle (Oazella subgtUturosa), from Kirkuk,

Perso-Mesopotamian frontier. The gazelles are
very widely distributed and the numerous species

LIST OF ILLUSTRATIONS xv

PIG.

are found in a great variety of different tjrpes of
country. (Drawn from life by Miss A. M. Gayton) p. 91

38. Holes of Dipodomys deserti in Sandy Ground, Mellen,

Arizona. (Photo : Dr. J. Grinnell, Museum of Verte-
brate Zoology, University of California) facing p. 102

39. Fore-feet of the following Lizards : —

A. PhrynocephaliLs mystaceus ( X 1 J)

B. Acanthodactylus scutellatus ( X 2)

C. Scaptira grammica ( X 2)

D. Callisaurus ( Uma) scoparius. (After Cope, *' Amer.
Nat.," 1894.)

E. Teratoscincus scinctis ( X 2)

F. Stenodactylus guttatiis ( X 3)

G. Ceramodactylus dorice ( X 3)

(E. Terzi) . p. 119

40. Hind-feet of the following Lizards: —

A. Phrynocephalus mystaceus (X IJ)

B. Acanthodactylus scutellatus (X 2)

C. Scaptira grammica ( X 2)

D. Callisaurus (Uma) scoparius, (After Cope,
"Amer. Nat.," 1894.)

E. Teratoscincus scincus (X 2)

F. Stenodactylus guttatus (X 3)

G. Ceramodactylus dorice ( X 3) . . . p. 120

41. Giant Cactus (Cereus giganteus), in which were found

Nests of Gilded Flicker and Screech Owl : near
Potholes, Colorado River, California. (Photo : Dr.
J. Grinnell, Museum of Vertebrate Zoology, Univer-
sity of California) . , . . facing p. 130

42. Typical Black Diurnal Tenebrionid Beetles of the Great

Palsearctic Desert. A and B, Adesmia ulcerosa; C
and D, Pimdia angulata. (E. Terzi) . facing p. 150

43. Typical Black Diurnal Flies, from Palestine, belonging

to different Sub-families of the Bombyliidae: (A)
Bombylius fuscus (Bombyliinse) ; (B) Hemipenthes
(Anthracinse) (near H. velutina). (E. Terzi) facing p. 152

ANIMAL LIFE IN DESERTS

CHAPTER I
THE DESERT CLIMATE

i. General, ii. Water, iii. Heat. iv. Relative Humidity.
V. Wind. vi. Evaporation, vii. Light, viii. Summary.

i. General
A prominent authority has stated that the desert
occupies one-fifth of the surface of the globe, an
area equal to that of Africa. It is probable that
the word desert was used in rather a wide sense,
and it is certain that no one has yet arrived at a
definition of the word which would be acceptable
either to the biologists or to the meteorologists.
One is accustomed to think of the desert as an
area of the earth rendered unfit for normal life by
its climate, but, as I hope to show later, there is
no climatic factor, or combination of climatic fac-
tors, which invariably produces desert ; in fact, a
few deserts exist by reason of their geological
constitution, though their climate is not particu-
larly unfavourable to plant and animal life. As the
causes which result in desert are diverse, it follows
that the term is not capable of strict definition :
the definition which I now put forward is admittedly

1 B

2 ANIMAL LIFE IN DESERTS

unsound, because it looks not to the forces which
produce the desert, but to the result of their action;
not to the weather and soil, but to the plants and
animals which can grow in the desert in spite of
its physical conditions. I use the word " desert "
to include places in which the climate is hostile
to animals and plants, in which normal agriculture
is impossible, and in which nearly all the existent
forms of animal and plant hfe are modified to endure
life in their pecuHar environment. I use the word
" semi-desert," without exact definition, to describe
country of which the climate is less hostile, and
the flora and fauna less specialized, than that of
a desert ; semi-deserts support cultivation at cer-
tain seasons, and provide grazing, though it is
often bad grazing, at all seasons. Let us also bear
in mind that deserts grade quite imperceptibly
into semi-deserts, and these into savannas, steppes,
and downs, and that a country may be extreme
desert at one season and covered with lush vegetation
at another. Furthermore, deserts are not neces-
sarily permanent or very ancient ; the buried
civilization of Eastern Persia and Turkestan and
the petrified forest near Cairo are sufficient evidence
of this.

Most of the extensive deserts lie a little to the
north of the northern tropic, or a little to the south
of the southern tropic ; they do not lie close to the
Equator. Most of them lie in the northern hemi-
sphere and are bounded northwards by steppe,
that is to say, arid country with a covering of
grass and other perennials and an abundant flora

THE DESERT CLIMATE 3

after the winter rain, and southwards by savanna,
that is to say, arid grass land with a few trees.
The largest of all deserts is practically continuous
from the Atlantic coast of North Africa to North-
west India and the heart of China. It includes
the whole of Northern Africa down to about lati-
tude 20° N., but excluding those parts of Morocco,
Algeria, and Tunisia which border the Mediterranean :
it includes also Egypt and Sinai ; Arabia, the
Syrian Desert, and Mesopotamia ; Persia, Afghani-
stan, and Baluchistan ; Transcaspia, Turkestan, and
the Gobi Desert, in Central China ; and parts of
the Punjab, Sind, and Rajputana. The whole of
this vast area is inhabited by the same types of
animals and plants, and these for the most part
are derived from Europe and Northern Asia, and
to a much smaller extent from equatorial Africa
or peninsular India. The great desert is, in fact,
an integral part of the " Palsearctic Region," which
is one of the primary divisions into which zoolo-
gists and botanists have divided the globe : this
region includes all Europe, and Northern and
Western Asia, and Africa as far south as the southern
part of the Sahara (about latitude 20° N.). I pro-
pose, therefore, to use the term " Great Palsearctic
Desert " when referring to this tract.

The great desert of Australia is probably the
second in the world in point of size ; it includes
the heart of the continent and reaches nearly to
the west and south-west coasts.

The North American deserts consist of several
small areas in the southern and south-western

4 ANIMAL LIFE IN DESERTS

States of the Union, and in Mexico. The impor-
tance of these deserts to the botanist, and in a
secondary manner to the zoologist, lies in the fact
that they have been more thoroughly studied than
any other desert region in the world. The labora-
tory at Tucson, Arizona, supported by the Carnegie
Institution of Washington, and directed by Dr.
D. T. Macdougal, has contributed immensely to
our knowledge of the climatic and physical features
of the surrounding deserts, and of the influence
of these features upon the vegetation.

Other desert areas are found in South- West
Africa and along the coast of South America,
from latitude 5° to 30° S., in Eastern Patagonia
and Western Argentina. Quite small areas of
desert occur in many parts of the world, and any
area of sand dune very closely resembles desert
in the scarcity of available moisture, and in the
specialization of its flora.

It is not to be understood that any area described
above as desert is uniformly so, either in its physical
condition or in its flora and fauna. In the belt
occupied by the Great Palaearctic Desert there are
certain very fertile spots, for example, the delta
of the Nile, the highlands of Yemen, and the date
groves of Basra, and a similar diversity is found
in other desert regions.

We shall now review the chmatic influences
which contribute largely to make life in a desert
impossible to any plant or animal which is not
specially adapted to it. In the mind of every one
the desert stands first for dryness, secondly for

THE DESERT CLIMATE 6

heat ; and though this conception is not strictly-
accurate, I propose to be guided by it. I shall
therefore deal first with the supply of water and
second with the heat and cold experienced in
deserts. The available moisture and the current
temperature together determine the amount of
water-vapour present in the air, and I shall deal
with this next. This will be followed by some facts
relative to winds, because air movement is the result,
in part at any rate, of the rapid fluctuations in the
temperature to which these bare spaces are sub-
ject. The discussion of wind leads us naturally
to consider evaporation, which results from the
presence of moisture and the combined action of
heat and of air movements. The meteorological
statistics which are quoted do not give very accurate
information of the conditions to which the desert
plants and animals are exposed. The instruments
with which they are taken are generally exposed
in a ventilated white-painted screen : the organisms
which we are studying live on the surface of rocks,
and in holes, and in a variety of other natural
habitations.

ii. Water

It may be admitted at once that relative lack of
moisture is a characteristic feature of all deserts,
but it is not possible to state dogmatically that if
the rainfall be below a certain figure the land will
be desert, because the condition of the land depends
not only upon rainfall but on many other climatic
factors. It is generally accepted that a rainfall

6 ANIMAL LIFE IN DESERTS

of less than 5 inches (127 mm.) a year always pro-
duces desert. On the other hand, there are areas
between the Pacific Ocean and the Californian
ranges of mountains, and in the Jordan Valley,
which are desert though they receive 18 inches
(460 mm.) of rain. In the first area the causes
are the very high winds to which it is exposed,
and the fact that most of the rain falls in winter,
when it is of little service to the plants. In the
second area, the lower end of the Jordan Valley
and the land round the Dead Sea, the cause is the
salinity of the soil. One concludes that it is un-
profitable to devote much attention to the mean
annual rainfall because the number of inches re-
ceived is of less importance than certain peculiarities
in its distribution through the seasons and through
successive years, and because such factors as soil
and exposure are also of prime importance.

The rainfall in deserts is always very unevenly
distributed throughout the months and the seasons,
and unless one or more dry seasons of several
months' duration occur, the condition of the land
is not desert or even semi-desert. The graph
(Fig. 1) shows the seasonal distribution of the
rainfall which is characteristic of most places in
the Great Palsearctic Desert. It will be seen that
there is a dry or nearly dry season in summer,
averaging six months, and a relatively wet season
in winter. In the deserts of South Australia a
similar alternation of dry hot weather and wetter
cold weather occurs with regularity.

The fact that the rainless period and the hot

THE DESEET CLIMATE 7

period coincide is of great importance to the vege-
tation, which has to protect itself simultaneously
against drought and heat : furthermore, the dry
and hot period is very long.

Within the limits of the Great Palsearctic Desert
there are a few places which do not have a cold

XII I II ill IV V VI VII VIII IX X XI XII
3 in.T — ' ' — ' — ' ' ' ' — ' — ' — ■ — ' — r 75(u m.

SOmm

25 mm.

Tashkent.TurKestan

> Baghdad, Mesopotamia.

o.oooChaman. Baluchistan Port Said, Egypt.

Bahrein. Persia.

Fig. 1. — Average Monthly Rainfall of Five Places in the Great
Pal^iarctio Desert.

wet season and a hot dry season. The area of the
Indian desert (Fig. 2), in Rajputana, Sind, and the
Punjab, is an exception, as owing to the monsoon
the majority of its rain falls in July or August :
in most stations in this area a small fall of rain
occurs also in early spring.

XII

ii iir IV V VI VII VIII IX X XI XII

XII III VI , IX Xlt

Multan, Punjab Montgomery. Punjab. Jaisalmer.Rajputana.

Karachi, Sind. » » . » o Dera Ismail Khan, N.W.F. Province.

Fig. 2.

-Average Monthly Rainfall op Five Places in the Indian
Desert.

THE DESERT CLIMATE

At many stations in the North American deserts
the distribution of the rainfall resembles that which
has just been described in the Indian desert (Fig. 3).
The heaviest fall occurs in the summer, and a
definite winter rain occurs in many places, so that

XII I 11 III IV V VI VII VIII tX X XI XII
ain.T"-' — ' — ■ — ■ — ' — ' — ■ — ' — ' — ■ — ■ — nbm.

-50 mm.

25 mm.

oo ceo Tucson, Arizona
- - S^George. Utah

Fort Mohave, Arizona.
Calexio, California.

Fig. 3.

-Average Monthly Rainfall of Four Places in the Deserts
OF THE Southern States of the U.S.A.

The distribution of rainfall shown in this graph is not characteristic of stations in every part

of these deserts.

there are two short dry seasons, in early summer
and in autumn, in the North American and in the
Indian deserts. At a large number of stations in
the arid parts of North America only one rainy season
is recorded, either in midsummer or in midwinter.
So far, then, as moisture is concerned the conditions

10 ANIMAL LIFE IN DESERTS

in the deserts of India and in some of those of North
America are much less rigorous than they are in
most parts of the Great Palsearctic Desert : firstly,
because the season of great heat is not also the
season of great drought ; secondly, because the
periods of drought are shorter as there are two dry
and two wet seasons in the year ; and, thirdly,
because in the majority of stations a little rain falls
in nearly every month of an average year. If the
rainfalls which are shown graphically in Figs. 1-3
are studied it will be seen that either one or two
dry periods per year is characteristic of all the
places. In certain places these dry periods are
much more extended, for the precipitation is quite
irregular in its occurrence, and an intense desert
results. Hayward found mimosas dead at Kidal in
the South Sahara after five years without rain ;
one must suppose that, as trees had been able to
grow, the normal conditions were not utterly
unfavourable to plant life, but an unusually long
dry spell killed, no doubt, not only the mimosas but
other plants as well, and with each plant species a
host of insects, spiders, and other animals dependent
on it. A year after Ha3rward made his journey
across the Sahara Hartert was in Tidikelt, in the
Central Western Sahara (1912). He found that
rain had been very deficient for twenty years and
as a result the Chenopodiaceous plant Traganum,
which Rohlfs found growing in thickets in 1864,
had died completely, even to the very roots.

Mrs. Forbes has recorded that when she was at
Kufara (Libya) in 1921 no rain had fallen for seven

THE DESERT CLIMATE 11

years, and it is probable that throughout a great
part of the Libyan Desert and of the Western Sahara
the rainfall is so slight and so irregular in its occur-
rence that it makes little difference to the plant
Hfe. Such plants as exist at all, and they are very-
few, are dependent on subsoil water.

Prolonged droughts have been recorded from
many other deserts. As we have seen, the rainfall
in the American deserts normally falls twice yearly,
and is distributed through nearly every month : in
spite of this it is on record that no measureable
rain fell at Bagdad, California, from October 3, 1912,
to November 8, 1914 ; a drought of over a year
occurred at Indio, California, from November, 1893,
to January, 1895.

It may be stated as a general rule that the rainfall
in desert places, even in places in which it is relatively
regular, is liable to very great variation from the
monthly and annual averages. This variation in-
tensifies the struggle between the plants and animals
and their environment, and is an important factor
in the production of a desert. Angot suggested that
the ratio between the maximum and the minimum
annual rainfall of a spot could be used as an index
of its agricultural possibilities. He believed that
conditions were very unfavourable to agriculture in
places in which the annual minimum rainfall was
less than one-third or one-half of the annual maxi-
mum. It is known, however, that an even greater
disproportion than this can occur in places which
are by no means desert, and we cannot say that a
great irregularity in the amount of annual rainfall

ANIMAL LIFE IN DESERTS

is found only in desert areas or that it is an invariable
characteristic of the desert climate. It occurs very
generally in the more pronounced deserts, and the
following are striking examples :

Annual Rainfall, inches.

Place.

Ratio

(max. = 100).

Min.

Av.

Max.

Salton Sea, California

trace

2-74

0-1 : 100

El Paso, Texas ....

2-20

9-23

18-30

120 : 100

Yuma, Arizona ....

0-60

3-26

11-41

5-3 : 100

Mohave, California .

2-20

4-97

21-34

10-3 : 100

Tucson, Arizona ....

5-26

11-58

24-17

21-7 : 100

Wargla, Algerian Sahara

nil

3-55

8-27

0-0 : 100

Beni Ounif , Algerian Sahara

0-50

8-50

5-9 : 100

Baghdad, Mesopotamia . .

2-00

7-29

17-30

11-6 : 100

Basra, Mesopotamia . .

210

6-60

10-70

19-9 : 100

Roeburn, Australia . . .

013

0-32 : 100

It might be supposed that the number of rainy days
per month or per year would be closely correlated
to the monthly or annual precipitation, but this is
not the case, for very great variation occurs in the
amount of rain which falls on the average rainy
day. In some desert climates it falls in minute
amounts, and the number of rainy days may therefore
be relatively large. This is characteristic of the
South AustraHan Desert. At Oodnadatta, for in-
stance, one-third or even one-half of the annual
precipitation (4-68 inches : 118 mm.) is in amounts
of less than 0-15 inch (4 mm.) : such minute
amounts of water do not moisten the soil to an
appreciable depth, and are very quickly evaporated.

THE DESERT CLIMATE

unless one minute fall rapidly succeeds another.
We need to distinguish between the actual rainfall
and that part of it which reaches the roots and so
becomes available to plants, and subsequently to
animals.

In other desert climates the opposite condition
occurs, for the rain falls in large amounts on a very
few days in the year. This is characteristic of very
many deserts and may be so extreme that a single
day's downpour exceeds the total rainfall of an
unusually dry year. As examples one may quote
the following figures :

Place.

Annual Average

Day's abso-
lute Maximum.

Month.

in.

mm.

in.

mm.

Bairam Ali
Golodnaia Steppe
Andijan ....

Basra

Amara, Mesopotamia
Jodhpur, India .

505
1105

9-60"

6-60

8-0
13-63

128
278
242
167
203
347

1-62
3-97
2-91
3-10
6-75
10-00

101

171

253

March

November

October

November

August

Such excessive rainfall is comparatively un-
available to plants and animals because a great
proportion of it runs off the surface of the ground
into the river beds, and only a small part soaks into
the soil at the place where it fell. The torrent
which is produced in the stream bed is extremely
destructive to plant and animal life (page 50). I
conclude, then, that statistics of the average number
of rainy days per month, or year, or of variation

14 ANIMAL LIFE IN DESERTS

from that average, give little information to the
biologist.

It is probable that dew is of extreme importance
to the desert flora and fauna, but as practically no
reliable statistics relating to actual dew-fall have
been published, I am compelled to leave the matter
in a very unsatisfactory state. It would be of great
interest to biologists if i^eteorological observatories
situated in deserts would accumulate information as
to the amount of dew which actually falls under
natural conditions, and the seasons and regularity
of its fall.

To sum up, the ordinary meteorological statistics
are enough to assure us that the aridity of deserts
is great ; they do not, however, tell us the whole
truth, for three reasons. The first is that much of
the recorded rainfall is not to be reckoned as " avail-
able moisture," because a large proportion falls in
heavy downpours which run off the surface of the
ground into the water channels, and in some places
an equally large proportion falls in such small
amounts that it fails to penetrate the soil before it is
evaporated. The second reason is that rain which
faUs in the cold season, when vegetation is inactive,
is of little value to the plants ; the third, that from ^
year to year the climate deviates widely from the
normal. A certain flora may adapt itself to grow
in a given spot, but may be exterminated by several
unusually severe summers, after it has been estab-
lished for several years. Shortage of water, and
particularly shortage at seasons when the plant's
requirements are large, is a most important factor

THE DESERT CLIMATE 15

in the production of deserts, but is by no means the
only factor, and under certain circumstances places
can be utter desert in spite of receiving a liberal and
not ill-distributed supply of water.

iii. Heat

The temperature is of fundamental importance to
the flora and fauna, not only for its own sake, but
because it influences the humidity of the air and the
evaporation of moisture. It is generally realized
that the climate of a desert may be intensely hot ;
it is equally true, though not so well known, that it
may be extremely cold. Considerable daily and
yearly range of temperature is a characteristic of
the chmate of all great land areas, and we are
justified in presuming that the extremes of tempera-
tures of the desert are partly due to the fact that
most desert areas lie in the centre of large land
masses. This presumption is supported by the fact,
to which we shall return later, that desert areas
which lie close to the sea are not subjected to
extremes of heat and cold. But we must not
attribute the range of the temperature exclusively
to the continental position of deserts, because the
extremes encountered in deserts are much greater
than they are in other continental areas ; and we
beheve that the very great fluctuations of tempera-
ture are due very largely to the bareness of the soil
and the clearness of the sky. The radiant heat of
the sun is not impeded either by cloud or by vegeta-
tion from striking directly on the soil, which is

ANIMAL LIFE IN DESERTS

warmed very rapidly to a high temperature. The
hot surface of the earth then warms the lower layers
of the atmosphere by conduction, and produces
high air temperatures. At night, on the other hand,
there is no blanket of vegetation to hinder loss of
heat from the ground. Therefore much of the heat
which has accumulated during the day in the

Fig. 4.

Xli I II

IV V VI VII VIII IX X XI Xl>

40^

^ Wadi Haifa. Egypt. Helwan, Egypt

Babylon, Mesopotamia.

-Average Monthly Mean Shade Temperatures op Three
Places in the Great Pal^la.rctic Desert.

superficial layers of the soil is radiated into space
between sunset and sunrise.

The monthly average temperatures of certain
desert stations are shown graphically in Fig. 4.
Two things are apparent : very high temperatures
are attained in deserts, higher in fact than are ever
reached in many places closer to the Equator, and
very wide annual ranges of temperature are char-

THE DESERT CLIMATE

acteristic. Almost any place in any desert will
show these essential characteristics of the desert
climate, provided it is not close to the sea.

The contrast between a hot summer and a cold
winter is shown not only by mean figures, such as
those on which Fig. 5 is based, but even better by
quoting the extremes of temperature which have
been recorded at a given spot either in one year or
in a series of years. The following are good
examples :

Place.

Period

Absolute Range.

^'C.

Mosul, Mesopotamia ....
Baghdad, Mesopotamia .
Petroalexandrovsk, Turkestan .
Tashkent, Turkestan . . .
Ghardaia, Algeria ....
Kasalinsk, Turkestan . .

7 years

28 „

10 „

1 year

1 „

66-5
57-8
71-8
70-2

57
88

119
104
128
126
102
158

The following figures from Wadi Haifa (Anglo-
Egyptian Sudan) are interesting because they show
that though the normal range of temperature is
great the occasional range is very much greater :
the coldest month is January, with a mean lowest
reading of 7-8° C. (46° F.); the absolute lowest
reading in twenty-one years was — 2-2° C. (28°
R); the mean highest reading is 41-1° C. (106° F.)
(June), the absolute highest being 52-5° C. (130° F.)
in April. It is clear that a slight frost, occur-
ring once in a score of years, at a place in which
the thermometer does not pass below 7-8° C.

XII I II

IV V VI vn VIII IX X XI XII

.♦- '-•♦♦'

♦^ ,♦

■25

^^ Jacobabad, SInd. — — Ghardaia, Algerian Sahara.

Chaman. Baluchistan. ♦♦♦♦♦> Nukus, Turkestan.

-20

-30

Fig. 5. — Monthly Mean Maximum and Mean Minimum Shade Tem-

PERATUBES OF FoUR PLACES IN THE GrEAT PaL^EARCTIC DeSERT

THE DESERT CLIMATE 19

(46° F.) in an average year, might devastate the
flora.

The daily range of temperature is scarcely less
striking than the yearly, and is characteristic of all
desert areas except those in close proximity to the
sea. Cannon quotes figures which show that the
extreme daily range of temperature recorded during
three years at In Salah and Wargla in the Algerian
Sahara is about 36-40° F. (20-22° C.) in the winter
months and about 50-52° F. (28-29° C.) in the
summer months. The average range of temperature
on a single day in Baghdad, Mesopotamia, is 21° F.
(11-7° C.) in January and December, and 31° F.
(17-2° C.) in August and September. But though
the daily fluctuation of temperature is generally
highest during the hot months it appears that the
greatest range which has ever been recorded in a
single day was observed in December at Bir Milgha
in Southern Tripoli by Rohlfs : he recorded a range
of 68° F. (37-8° C), from 31° F. to 99° F. (- 0-5° C.
to 37-2° C), within twenty-four hours.

Many other instances of extremely rapid change
of temperature are on record : Paulsen observed the
shade temperature to be 37°, 68°, and 82° F. (3°, 20°,
and 28° C), at 6 a.m., 9 a.m., and 1 p.m. in sand
desert in Transcaspia. He also records the following
figures at Tachta, on the Murgab River, on the
23rd of June :

6 a.m. Shade temperature 78° F. (25-5° C). Sun temperature

93° F. (34-0° C.)
8 a.m. Shade temperature 85° F. (29-5° C).

20 ANIMAL LIFE IN DESERTS

11 a.m. Shade temperature 104° F. (40-0° C). Sun tempera-
ture 122° F. (50° C.)
3 p.m. Shade temperature 109° F. (43-0° C). Sun tempera-
ture 129° F. (54° C.)

It wiU be noticed that enormous fluctuations in
the temperature of the day, and of the year, are
generally recorded from such places as Kasalinsk,
Petroalexandrovsk, and Tashkent, in which the
effect of desert conditions is reinforced by a position
in the centre of a great land mass. On the other
hand, certain places which are close to the sea are
not liable to extremes of temperature, but are
veritable deserts. Fig. 6 shows the monthly average
maximum and minimum temperatures of El Arish,
Aden, and Bahrein, all of which are in desert areas,
on the coast of the sea. One concludes that great
daily and annual range of temperature is a common
element of desert climates, but not an essential
characteristic. The bright sun shining unimpeded
on the desert soil heats it very rapidly, so that
by midday the temperature of its surface greatly
exceeds that of the air above it.

Our knowledge of the temperature reached by
the surface of the soil is slight, but I hope shortly
to publish records which show that in summer in
South Palestine the surface of clay desert rises about
36° F. (20° C.) beyond the shade temperature at
midday. Nearer the Equator no doubt even higher
readings would be secured, but in Palestine surface
readings of 122-140° F. (50-60° C.) are normal.
Prezhevalsky has recorded similar figures for the
Gobi Desert, and adds that the surface of the soil

THE DESERT CLIMATE

may be as cold as — 16° F. (—26-5° C.) in winter.
The highest readings which have so far been taken
of the surface of the soil were taken on bare sand ;
e.g. readings of 183° F. (84° C.) on the Loango
Coast, close to the Equator, and Augieras' record of
172° F. (78° C.) on a sand dune in the Sahara. The\
surface soil reaches such a high temperature by day

F XII I II III IV V VI VII VIII IX X XI XII

El Arish, Sinai. Aden, Arabia.

Bahrein, Persian Gulf.

Fig. 6. — Monthly Mean Maximum and Mean Minimum Shade Tem-
peratures OF Three Places situated on the Sea Coast of the
Great Paljearctic Desert.

that it does not cool completely during the ensuing
night : as a result the minimum temperature
reached by the surface of unshaded soil at night may
be several degrees above the minimum temperature
of the air (C. B. WilHams). It is only the superficial
layer of the soil which is liable to these great fluctua-
tions of temperature.

22 ANIMAL LIFE IN DESERTS

At Tucson, Arizona, in June, the temperature
ranges daily through about 17° F. (10° C.) at a
depth of 6 inches (15 cm.) in the soil, and over about
2° F. (1° C.) at a depth of 10 inches (25 cm.) ; at
the same season the shade temperature ranges over
about 57° F. (37° C). Therefore at 6 inches (15 cm.)
the daily fluctuation is about one-quarter of that
of the air, and at 10 inches (25 cm.) it is only about
one-thirtieth. Results which are essentially similar
have recently been obtained by C. B. Williams in
the desert near Cairo, Egypt, in July. The same
investigator sends me the following data taken in
April, 1922, at Luxor, Egypt, on cotton land which
had been irrigated three weeks previously : air
temperature 86° F. (30° C), soil surface 131° F.
(55° C), soil at 3 inches (7-5 cm.), 81° F. (27° C.) ;
at the same time the relative humidity of the air
was about 15 per cent., and the relative humidity
3 inches deep in the soil 98 per cent. These observa-
tions may be taken as typical of others which have
been made in South Algeria and other deserts. It
will be seen that an animal would very easily reach
equable conditions by burrowing, and that it would
pass through a very great range of temperature and
humidity as it entered or left its burrow during the
middle of the day.

iv. Relative Humidity

The rainfall and the temperature of the desert
have been discussed : upon their interaction depends
the relative humidity of the air. It is defined as the
amount of water- vapour which the air contains com-

THE DESERT CLIMATE 23

pared with the amount which it would contain if it were
saturated with moisture from a flat surface of water
at the same temperature. Relative humidity might,
of course, be expressed as a vulgar fraction ; we could
say that it was " one-third," meaning that the air
contained a third of the amount of water-vapour
which it could hold if saturated at the particular
temperature under discussion. But it is generally
more convenient to express the humidity in per-
centages, the figure 100 representing saturation.
The amount of water- vapour which the air can hold
varies very greatly with the temperature, and it
rises constantly as the temperature rises, so that a
much greater amount of water-vapour is required
to saturate a certain volume of air when it is warm
than when it is cold. Suppose, for instance, that
the air is saturated with water-vapour in the cold
early morning, and that the actual amount of
moisture in the air remains constant throughout the
day : then the relative humidity will fall steadily as
the temperature rises, because the air when warm
could contain much more moisture than it actually
does contain.

This is what happens in most parts of the world
on most days in the year. Among masses of dense
vegetation and in damp places it is hardly noticeable
because, however warm the air becomes at midday,
it can still saturate itself from the wet soil and the
vegetation. But in deserts the difference between
midday with its low relative humidity, and the night
with its high relative humidity, is extremely pro-
nounced, because, as we shall see later, fl.uctuations

ANIMAL LIFE IN DESERTS

of temperature are excessive, and there is little
moisture available to increase the humidity of the
air when its temperature rises. There is, therefore,
a great contrast between the forest type of climate,
with a very constant humidity, and the desert type,
in which the humidity fluctuates widely in each
period of twenty-four hours.

In point of fact such a range of relative humidity

Monday -^mt— -Tuesday >f<^- Wednesday-^

19 P.!4t r2 24 12 I

Fig. 7. — Curve obtained from Recording Instrument showing Daily
Fluctuation in Relative Humidity at Gizeh, Egypt, 20th-22nd
March, 1922.

The figures on the side of the graph represent percentages of humidity. (C. B. Williams.)

as is shown in Fig. 7 does not occur from one year's
end to another in many tropical forests, yet at
Gizeh, Egypt, it is a normal daily occurrence during
the summer. The curve of which Fig. 7 is a repro-
duction was actually made during the end of March,
1922, and shows that the humidity can drop from
saturation to 20 per cent, in a few hours. Fig. 8,
which shows the daily fluctuation (8 a.m. and 4 p.m.)

THE DESERT CLIMATE

of relative humidity at Mosul, Northern Meso-
potamia, during an average week in June and an
average week in December, shows this point equally
clearly. Very similar figures are obtained if the

Sun. Mon. Tues: Wed. Thurs. Fri Sat.

484848484848

Fig. 8. — Relative Humidity at Mosul, N. Mesopotamia, at 8 a.m. and

4 P.M. DURING AN AVERAGE WeEK IN JUNE AND AN AVERAGE WeEK

IN December.

mean of a series of readings is taken. Fig. 9 repre-
sents the mean relative humidity taken at intervals
of two hours every day from June to September,
at Mohammerah, near Basra. The daily fluctuation
in the humidity is, of course, less striking because

ANIMAL LIFE IN DESERTS

this figure is based on average readings for that
period, and the fluctuation would be even more
remarkable were figures available, not from Moham-
merah itself, which is on the Karun River among
date palms, but from a spot two or three miles from
it in bare desert country.

Relative humidity varies very greatly within very
short distances. Observations taken among a few
palms, or in a cave or house, show a humidity
very much less variable and generally higher than

6?..n. 8ajii lOam. IZfwon Zptm. 4 p.m. 6p.m.

Fig. 9. — ^Mean Relative Humidity at Two -hourly Intervals for the
Months June, July, August, and September at Mohammerah,
Persian Mesopotamia.

that which is prevailing a few yards away in open
desert.

It is generally true that the greatest fluctuations
in relative humidity occur during summer, and this
depends largely on the fact that the temperature
fluctuates more during a summer day than a winter
day (page 19). Rapid and wide alterations in the
relative humidity are therefore one of the many
chmatic factors which combine to attack both plants
and animals in summer, in deserts.

THE DESERT CLIMATE 27

The ordinary statistics of relative humidity pub-
lished by official meteorologists are very unsatis-
factory for the biologist. In many places readings
are only taken in the morning and evening, and the
full stress of extremely low humidity which oppresses
the flora and fauna at midday passes unrecorded.
Furthermore, readings are often taken at a place
convenient to the observer, seldom out in the desert,
and the readings of humidity suffer perhaps more
than any others because of the variations which
occur between places a few yards inside or outside
an oasis. It is also to be remarked that readings
are sometimes taken at 8 a.m. and 8 p.m., the two
times at which the humidity is changing most rapidly.
If, therefore, the reading is taken a few minutes
too soon or too late a considerable error may be
produced.

V. Wind

Rapid fluctuation in the temperature of the surface
of the desert, and of the air above it, results in air-
currents, which are generally greater in summer than
in winter. At any rate, in the Great Palaearctic
Desert a calm during the middle of the day is rare,
and in many places winds of constant direction are
experienced at this season. The sirocco is a hot
easterly or southerly wind which blows in Palestine,
Algeria, and other parts of the Mediterranean littoral ;
the shamal, in Mesopotamia, blows from the north-
west for many days at intervals all through the
summer. During June, July, and August, which

28 ANIMAL LIFE IN DESERTS

are the windiest months of the year, 75 per cent, of
the wind, and an even higher proportion of the
stronger winds, are from this quarter. The sirocco
and the shamal are two examples of the strong
winds from a certain quarter, which blow with
regularity in many deserts, but other and more
violent regular winds are on record.

At Menjil in North- West Persia a wind of great
violence and regular occurrence blows whenever the
sun is shining brightly on the Persian plateau. It
is caused by the rising of the air which has been
warmed by the hot plateau, and the consequent
inrush of unwarmed air from the surrounding areas.
At Menjil this is concentrated in the gorge of the
Safid Rud, a river which here cuts its way through
the Elburz Mountains, and a constant violent wind
blows through the gorge all the day long, throughout
the summer. This wind is of such strength that one
can only walk against it with the greatest difficulty,
and I have seen a loaded camel entirely unable to
make headway against it ; tents can only be pitched
during the hours of relative calm in early morning
and late evening, and when securely pitched are
generally ripped to shreds. Even more violent winds
have been experienced in many desert areas, but
few of them are of such regular occurrence as the
Menjil wind. Augieras, for example, has recorded
that in February, 1915, a violent wind kept him
prisoner under the lee of a rock at Erg Chech in the
Western Sahara for no less than nine days, and a
month later he experienced a gale which carried a
camel saddle 200 metres. The effect of wind-driven

THE DESERT CLIMATE 29

sand upon rock is illustrated in Fig. 11 (facing
p. 42).

The hot air which rises from contact with the
heated desert sometimes makes its way upwards in
vortices, or dust-devils. The dust-devil is a rotating
column of air, and is generally seen on very hot days
on which a moderate breeze is blowing. It is very
sharply delimited, and owing to its load of debris,
dust, and bushes, it is easily visible. It moves
slowly about in the desert, following the direction
of the wind rather irregularly. The height of the
vortex is variable ; a century ago Lane measured
one of 750 feet in Egypt and saw others taller, but
the majority were shorter ; they were continuous
columns reaching up from the ground for several
hundreds of feet. Normand observed dust-devils
at Samarrah in Northern Mesopotamia, some of
which were at least 300 metres high, though only
about 5 metres wide at the base. Sometimes these
vortices lose contact with the ground, but maintain
their existence at very great heights. Flying officers
in Mesopotamia have encountered vortices of this
sort whirling upwards at a height of 5,000 feet above
the ground and still carrying dust and debris. Even
a very small dust-devil is violent ; I have had my
shirt stripped from my back by a vortex which
seemed to be only a dozen feet in diameter, and
during the operations in Mesopotamia and North-
West Persia it was no uncommon sight to see a
particular tent struck and emptied of its contents
by a small vortex, which left untouched other tents
only a few yards away. Larger vortices are much

30 ANIMAL LIFE IN DESERTS

more devastating ; in 1918 a very large camp at
Balad Ruz, north-east of Baghdad, was struck by a
dust-devil of unusual size, which carved its way
through the camp, leaving a lane in which not a
single tent was standing. Heavy articles of kit were
blown as much as 200 yards through the air, and
an officer of my acquaintance was scooped out of
his tent with all his camp furniture, and dropped
twice, the second time with several broken ribs.

The effect of wind on other climatic conditions
is various. A hot dry wind causes a rapid and
considerable drop in the relative humidity, and
generally a rise in temperature. Often, however,
the wind causes a drop in temperature, because it
mixes the lower layers of the atmosphere, which
have been heated by contact with the hot earth,
with the higher layers which have not been so heated.
A wind heavily laden with sand or dust, and blowing
for many hours on end, may cause a most marked
drop in the day's temperature, by shielding the land
from direct sunlight.

vi. Evaporation

Though on one hand the rainfall is meagre, on
the other the evaporation is excessive in all deserts
and at nearly all seasons. The rapidity with which
water evaporates, whether from the superficial layers
of the soil or from hollows in which it has accumu-
lated, is caused by the high diurnal temperatures,
by the direct rays of the sun beating down from a
cloudless sky on bare earth unprotected by a covering
of vegetation, and by the unimpeded action of the

THE DESERT CLIMATE

wind. Figures are available from a limited number
of desert stations giving the number of inches of
water which would be evaporated from an open
surface of water by the month or by the year. These
figures do not represent what actually happens in
the desert, because very soon after a fall of rain the
surface of the soil is dried and evaporation practically
ceases. But if they are taken in conjunction with
the figures for annual mean rainfall they represent
very vividly the discrepancy between the water
upon which the plants can draw and the desiccating
effect of the desert climate and sun. This ratio
between possible evaporation (e) and actual rainfall
(r) is of very great interest to biologists, and it is
probably one of the most important factors in
determining whether a place will or will not be
desert. So far as we know it is high in all desert
regions, and it is not high in regions which are not
desert.

The following examples show the very high pos-
sible evaporation in deserts, and the ratio between
this and the actual rainfall :

Place.

Yuma, Arizona .
Piute Dam, Utah
Tucson, Arizona .
Mohave .
Cahuilla, California

Rainfall

(Mean),

Inches (r).

3-26
8-61

11-58
4-97

17-35

Evapora-
tion,
Inches (e)

100

61-2

95
116

e/r.

30-7
7-1
7-8

19-1
6-7

Cannon has given the following figures, which
show that at Laghwat and Ghardaia the discrepancy

ANIMAL LIFE IN DESERTS

between rainfall received and possible evaporation
is immensely and irregularly increased in the summer
and autumn months, the very period when the other

Table showing the ratio between evaporation and rainfall month
by month in 1908, at two stations in the Algerian coastal zone
and two in the Algerian Sahara. Evaporation has been
calculated as from a free water surface. Readings from a
Piche evaporimeter have been corrected.

Jan.

Feb.

Mar.

Apr.

May.

June.

July.

Aug.

Sep.

Oct.

Nov.

Dec.

Gran . .

1-3

1-9

1-6

1-3

17-4

8-5

146

2-45

3-4

4-4

Algiers .

0-6

1-3

0-5

22-3

11-7

219

28-8

5-0

1-0

1-2

Laghwat

4-7

9-8

203

373

421

25-9

14-2

154

104

Ghardaia

8-9

233

81-4

629

38-9

699

166

25-6

66-9

23-2

49-7

225

forces of nature aU combine to make life impossible
for any plant or animal except those specialized for
life in a desert. The ratio is lower and less fluctuat-
ing in the coastal non-desert stations (Algiers and
Oran). Cannon states that if the annual evaporation-
rainfall ratio of the littoral zone be taken as unity,
that of the high plateau is 3-7 and that of the desert
(average of Laghwat, Ghardaia, and El Wad) is 18-6.
It will also be appreciated that in an unusually
dry year the evaporation-rainfaU ratio will be vastly
increased, so that, at a time when the mere drought
is pressing hardly on the flora and fauna, an increased
discrepancy between rainfaU and evaporation is also
thrown into the scale against them. If, for instance,
the normal evaporation-rainfall ratio for Mohave,
with a mean rainfall of 4-97 inches (125 mm.) is
19-1, then in the dry year with a rainfall of only
2-20 inches (55 mm.) the ratio would be 43-2, if we

THE DESERT CLIMATE 33

suppose that the evaporation in that particular year
was average. Judge, then, how great must be the
fluctuations in this important ratio in spots in the
Libyan Desert where the rain falls only once in
every four or five years, and where the evaporation
is believed to be 150 inches or over.

vii. Light

The uninterrupted sunHght of Egypt, even in
the winter months, is a thing which has arrested
the attention of every tourist. Accurate records
of the intensity of sunlight in deserts are scarce,
but one can at any rate recall a few general truths.
The sun's rays consist not only of light rays and
heat rays, but also of ultra-violet and other rays
which are known to exercise very definite influences
on living matter. All these rays, but particularly
the ultra-violet rays, pass more readily through
dry than through damp air ; their effect on plants
and animals is therefore much more potent in summer
than in winter, for in summer the days are longest,
the sun most nearly vertical at midday, clouds are
absent, and the amount of water- vapour in the air
at its lowest.

Viii. SUMMAEY

We have discussed individual elements of the
climate ; let us now try to consider the cHmate
as a whole, built up of these and other component
elements. If we were to study only the average
meteorological statistics for a number of places in
the Great Palsearctic Desert we should reahze at

34 ANIMAL LIFE IN DESERTS

once the great contrast between the summer and
the winter. The summer is rainless ; it is very-
hot by day but much cooler at night, and the rela-
tive humidity of the air varies very greatly in the
twenty-four hours ; the daily fluctuation in the
temperature of the air is exceeded by that of the
temperature of the surface of the soil ; the sky
is clear, the day long, the atmosphere dry, and the
sun vertical or nearly so at midday, and it foUows
that the effects of the sun's heat and chemical
rays are very great ; the winds are strong and
constant in direction, and occasionally violent and
destructive ; evaporation is extremely active and
far exceeds the amount of moisture received by
the soil. In every respect the climate in winter is
different from that in summer. It is information
of this sort which we shaU glean from mean
statistics, but they only teU us a part, and an
unimportant part, of the truth. It is not the
contrast between the seasons, immense though it
is, which is the essential character of the desert
climate.

Rather it is the extraordinary deviations from
the mean which mark out the desert chmate as a
thing quite distinct. It is to the maximum and
minimum figures, not to the means, which we must
look if we are fully to reaHze the difficulties with
which desert plants and desert animals have to
contend. It is not the regular succession of summer
and winter, however dissimilar, but the occurrence
of long droughts, torrential rains, unusual frosts,
violent whirlwinds, and other irregular phenomena

THE DESERT CLIMATE 35

that have prevented the covering of the ground
with vegetation and the peophng of the vegetation
with a normal fauna. It is also to be constantly
remembered that many different factors go to deter-
mine that land shall be desert : here it is drought,
there it is wind ; in other places, as we shall see
in the next chapter, it may be shifting sand, or
saHnity of the soil, or absence of drainage or of
humus.

CHAPTER II
THE SOIL AND WATERCOURSES

The physical environment of a creature includes
not only the climate of its habitat, but also certain
factors which may collectively be termed " geo-
logical." Among them are the type of soil on which
it lives, the flatness or hilliness of the country, and
its exposure to or protection from sun, wind, and
rain, and the existence of supplies of water other
than rain and dew.

The influence of the geological environment upon
the desert plants and animals is almost as important
as the influence of cUmate, though less attention
has been given to it. The prevalent notion that
deserts are uniform stretches of sand dune is entirely
erroneous, for desert soils exhibit a wide range of
chemical and of physical characters. The soil of
a desert is commonly gravel, or sand, or bare rock,
or sunbaked mud ; other types of soil are found,
and almost the only soils which never occur are
those which result from the presence of plentiful
vegetation, for instance loam and peat. The scarcity
of humus is probably an important factor tending
to prohibit all but a few specialized plants from
colonizing deserts; in fact this, and the general

THE SOIL AND WATERCOURSES 37

badness of the drainage, are common characteristics
of desert soil.

It is to be remembered that various types of desert
pass gradually into one another. Clay desert passes
by insensible steps through clay desert containing
a few stones to stony desert ; at the other end of
the scale stony desert may contain so many large
stones and so little fine soil that it is not far removed
from rock desert. Further, an area which is uniform
so far as soil is concerned may be bare desert in
one ' place, semi-desert or steppe in another, by
reason of the presence of windbreaks, or of different
exposure, or of other factors. One cannot draw
sharp lines of delimitation between the different
types of desert, nor between areas which are desert
and others which are semi-desert. The Hmits of a
desert are indefinite not only in point of space ; they
vary also with time. This is so characteristic a
feature, and so striking when one has actually seen
it, that I shall return to it again and merely state
in passing that bare earth tenanted by a few special-
ized plants and animals and exposed to the full rigour
of a desert summer may enjoy a delightful spring
during which it is carpeted with lush, unspecialized
flowering plants and teeming with bees and butter-
flies. For two or three months one may truly say
that the desert has vanished (Figs. 24, 25, facing
p. 58).

It is impossible to understand the relationships
between the soil of a desert and its flora and fauna
without understanding the powers which are
possessed by all soils, in varying degrees, of holding

38 ANIMAL LIFE IN DESERTS

water, of allowing it to sink through them, and of
raising it from lower levels by capillarity. In
general we may say that evaporation of water
from the sm^face of the desert soil is due to the heat
of the sun, the movement and dryness of the air,
and the nakedness of the earth. Evaporation
(page 30) exceeds rainfall in deserts, except in
very short periods in the year : therefore the sur-
face of the soil is normally quite dry. But at
short distances beneath the surface one frequently
finds a proportion of moisture which is surprising,
and the proportion rapidly increases at sHghtly
greater depths : it is impossible in a general dis-
cussion to quote figures, and the depth varies with
such factors as type of soil, interval since last rain-
fall, and the depth of the permanent moisture in
the soil. The explanation of the dryness of the
surface and dampness of the deeper soU is that
after the soil has been saturated by a fall of rain
the surface rapidly dries : this drying process
penetrates to greater and greater depths, becoming
slower and slower, because the action of wind
is cut off, and the diffusion of the damped air is
retarded by the superficial layer of soil which is
already air-dry. There is continual upward mov^
ment of moisture from the depths of the soil in
which water was accumulated when the rain fell,
and to which in certain cases water is brought
by seepage from springs, rivers, or water-bearing
strata. This upward movement depends on capil-
lary attraction, which enables the water to rise
above the level at which it would naturally lie, by

THE SOIL AND WATERCOURSES 39

penetrating the minute spaces between the soil
particles. There is then an upward movement of
water, from the subsoil, due to the capillarity, and
a downward movement of the level from which
evaporation is taking place in the soil. This down-
ward movement is slower the farther from the sur-
face it is taking place : at a certain point the
upward and downward movements balance one
another, and at this level the moisture in the desert
soil remains constant, unless equilibrium is upset
by fresh rainfall or increased evaporative power of
the air, or some other disturbing factor. These
facts have a practical appUcation. Cultivation of
arid land is sometimes rendered possible by the
employment of a machine which reduces the sur-
face of the ground to fine powder (" dust-mulch ").
This layer of fine powder, penetrated by corre-
spondingly minute air-spaces, decreases the upward
diffusion of the air which has saturated itself with
moisture in the soil. The decreased upward diffu-
sion results in decreased evaporation, and equili-
brium is disturbed, to be re-established nearer the
surface, at a point where the upward movement
of the moisture once again balances the lessened
evaporation. But as the moisture in the soil now
lies at a higher level it is possible to plant and raise
crops which could not have come to maturity
without the aid of the " dust-mulch " (Livingstone).
Bearing it in mind, then, that terms such as
" sand desert," " gravel desert," are not capable
of exact definition, or of exact geographical de-
limitation, let us turn our attention to some of the

40 ANIMAL LIFE IN DESERTS

commoner different types of soil of which the desert
may consist, and the various problems which have
to be faced by organisms which inhabit the sand,
or gravel, or rock, or mud.

The sand is in many ways the most hostile of
all environments. Its surface is very smooth, and
offers little impediment to the wind. As has
been said already, winds in any desert tend to be
strong, sometimes violent : in sandy desert their
action is unchecked by any obstacle. These winds
are detrimental to the plants ; they break leaves
and branches, they greatly increase evaporation
from the soil and transpiration from the plant,
and they carry abrasive particles of sand and soiL

As the surface of most sandy areas is frequently
in motion, even in the absence of sand-storms, it
is extremely difficult for plants to colonize them.
Young seedlings are overwhelmed, tender shoots
are damaged by blown sand, and roots are laid bare
to the sun. In certain places where the surface of
dunes is particularly unstable no vegetation of any
sort grows. In the Indian deserts, according to
Blatter and Halberg, the fairly copious monsoon
rains may temporarily consoUdate the surface of a
dune which at other seasons is unstable. SeedUngs
of various plants then spring up and, as the sand
dries, some individuals of certain species hold their
own, while the rest die. In all parts of the world
spots which are less wind-swept are colonized by
special plants, many of them grasses, which re-
semble the marram of our own coasts in their habit,
and after they have established themselves and to

THE SOIL AND WATERCOURSES 41

some extent consolidated the dune, a number of
other plants are able to take root. These all tend
to hold together the sand around their roots and
to protect the surface of the dune from the wind
and from evaporation. There is therefore a ten-
dency for the dune to become more and more
solidified and immobile, and more and more covered
by vegetation : each plant that grows and then
dies increases by a little the organic constituents
of the dune, and by that much decreases one of the
factors which render colonization of its surface so
difficult.

The relationships of sand to rain falling on it are
remarkable. Water which falls on its surface sinks
in with extreme rapidity, and to a considerable depth:
and the tendency for the water to rise by capillarity
is slight, because the sand-particles are relatively
large. Therefore the rain which falls on sand is
of no use to short-rooted plants. On the other
hand, as it sinks rapidly and as the surface of the
water remains at a considerable depth, loss by
evaporation is less than in any other type of desert.
In fact, the sand dune is a sponge, and most of
the water which it receives it holds. The con-
ditions favour long-rooted perennials rather than
other types of plant. The sparse fl.ora of a sand
dune in the Great Palsearctic Desert often consists
solely of perennial grasses and deeply rooted switch
bushes, but in parts of Transcaspia, where sand
overlies impervious loess at no great depth, quite
luxuriant vegetation grows even in summer
(Paulsen).

42 ANIMAL LIFE IN DESERTS

In places where sand overlies an impervious
rock, copious water is available for the cultivation
of deep-rooted plants, which flourish when once
they are established. Just to the south of Jaffa,
in Palestine, is a large area of shifting dunes, with
a sparse flora and fauna, closely adapted to their
environment. The land was in fact indubitable
desert until certain astute people discovered that
vines would grow luxuriantly in depressions among
the dunes. In these places water can be obtained
at all seasons by sinking wells to about 6-8 feet,
and when once the young vines are established
they grow well and produce grapes in the dry, hot
autumn, at a time when the dunes appear a little
more dry and barren than usual.

Another plant which grows well in deep sand is
the date palm. Its root system attains a remark-
able length while the plant is still yoimg and smaU,
and reaches deep-lying supplies of water. Hartert
and other travellers have described the conditions
of date culture at El Wed in the Algerian Sahara
(Figs. 10 and 12). The town and gardens are in
imminent danger of being overwhelmed by moving
dunes, and are constantly afflicted by violent sand-
storms. Subsoil water is plentiful at a considerable
depth in the sand, and the inhabitants excavate
large pits in the sand, and at the bottom plant
offsets of palms. At first watering by hand is
necessary, but after a few months the young palm's
roots reach the subsoil water : the owner's task then
is to remove the sand which threatens to cover
his trees, and at this task he labours almost un-

Fig. 10. — ^Datb Palms (Jiiuwing in Artificial Depressions in Sand Dunes
AT El Wad, S. Algeria. {Photo : V. H. W. Dowson. July, 1922.)

'£

Fig. 11. — Ridge of Cretaceous Limestone carved by Wind-driven Sand,
AT Umm Shersher, S. of Kharga Oasis, Libya. {Photo : F. W. Green,
Geol. Survey, of Egypt.)

THE SOIL AND WATERCOURSES 43

ceasingly with his basket ; he also dusts his vege-
tables with a small brush to free them from drifted
sand. Figs. 10 and 12 show clearly the contrast
between the flourishing palm which has tapped the
subsoil water, and the barren dunes which surround
it. The palm-leaves inserted in the sand in Fig. 12
are intended to check wind-driven sand: there is
no undergrowth because the water supply is so
deep.

The Nefud, or areas of sand dune in Arabia, are
relatively fertile and support so much indigenous
vegetation that they are recognized winter and
spring pastures. Camels grazing in the Nefud in
spring are able to dispense with drinking for long
periods. Doughty records that the inhabitants
planted a dune at Boreida with tamarisks, and that
after one year the trees were established and no
longer in need of artificial watering.

Sand deserts of various types may be distin-
guished : bare, shifting dunes, more stable dunes
covered with plants, and undulating plains. In
the desert west of the Nile, and in many other
places, areas of loose sand alternate with outcrops
of rock, and the rock is often etched and carved
with fantastic shapes by the wind-driven sand
grains (Fig. 11). Sand desert of one kind or
another is said by Cana to occupy 700,000 square
miles of the Sahara, an area equal to about one-
fifth of the whole ; according to Augieras, dunes
up to 200 metres in height exist in the Western
Sahara : no other area of equal extent is known.
The Takla Makan, in Eastern Turkestan, is a sandy

44 ANIMAL LIFE IN DESERTS

desert of considerable size ; Sven Hedin states that
he travelled for several days in it without seeing
any sign of vegetable life.

Deserts of clay, fine river silt or loess, present
contrasts to sand deserts in nearly every particular.
The soil is extremely fine in texture. The surface
is generally flat (Figs. 13 and 14) or nearly so,
smooth, and hard ; rain which falls upon it tends
to run off rapidly either into watercourses or into
depressions from which it rapidly evaporates. Fur-
ther, these finely grained soils have a high capacity
for holding water ; therefore that portion of the
rain which sinks into them does not penetrate to
a great depth, but is held in the superficial layers
of the soil and rapidly lost by evaporation. For
these two reasons soils of this type waste a large
proportion of the rainfall which they receive. For
a similar reason they are wasteful of any ground
water with which they may be endowed : as the
particles of the soil are very fine and the interstices
between them minute, the force of capiUary attrac-
tion exerted by them is great : ground water is
therefore carried up towards the surface and made
available for shallow-rooted plants ; but large
quantities of it are evaporated.

The ground water brings up with it mineral
salts, which are left in the supei-ficial layers of the
soil as it evaporates. The rain water, which runs
into a shallow depression and then evaporates, tends
to concentrate these salts in patches. As most of
these deserts are flat they are devoid of good sur-
face drainage, and as their soil is so fine in texture

— x

W -19^ ■ " ■ . ; ••; :i f V ..V V u V-l i t'T .

THE SOIL AND WATERCOURSES 45

and so consolidated, there is no subsoil drainage.
One finds therefore that some degree of saltness
is characteristic of flat clay or mud deserts. In
the parts which lie a little higher than the rest,
and from which the salt is washed by the rain,
the salinity is slight, and plants, many of them
specially adapted to growth in salt places, may be
found. In the depressions it is common to find
an incrustation of crystals of salts, and an absence
of vegetation of any kind whatsoever (Fig. 14),
or one may find that the ground is slimy, even in
dry weather, owing to the hygroscopic properties of
the salts which it contains. Around the margins
of these salt patches one finds an intermediate
zone inhabited by salt-loving plants, such as grow
at home on sea marshes. In Fig. 14 the plants
on the right are Suaeda : they are growing on land
which is a few inches higher than that on the left,
which is covered with white salt-crystals. Fig. 15
shows Atriplex halimus and other bushes which
love salt, growing on a plain of salt mud.

The salts found in these positions vary. Common
salt (sodium chloride) is, I believe, always present,
but in less proportionate amounts than in sea water.
In Transcaspia magnesium and sodium sulphate
are common, and calcium sulphate (gypsum) occurs.
In Mesopotamia different proportions of chlorides
and sulphates of sodium, calcium,, and magnesium
all occur in relatively large quantities, in the salt
and alkaline lands.

Figs. 16 and 17 show a peculiar type of salt
clay desert which is found at the lower end of the

46 ANIMAL LIFE IN DESERTS

Jordan VaUey, and in certain spots round the
margin of the Dead Sea. The soil here is so im-
pregnated with salts that in spite of an annual
rainfall of 16-18 inches, and in spite of the excellent
surface drainage provided by these slopes, no
vegetation exists. My friend, Mr. Raczkowski, of
the Department of Agriculture, Palestine, made
an analysis for me of the surface soil of one of the
hillocks shown in the plate ; the analysis was made
in February, just after the winter rains which one
might suppose would have washed much of the salt
out of the superficial layer of soil. Nevertheless,
the analysis revealed the presence of 0*58 per cent
of sodium sulphate, 0*57 per cent of sodium chloride,
and 36-13 per cent of sodium carbonate. Any
one of these salts in such high proportions would
be sufficient to prevent the growth of plants, except
forms specially adapted to exist on salt soils : their
united effect is to render these clay hills abso-
lutely devoid of plant life at all seasons of the
year.

The loess of Transcaspia and Turkestan and the
fine silt of the plains of Lower Mesopotamia are
very fertile if they are irrigated and if provision
is made for the removal of the water after it has
flowed upon the land, so that mineral salts do not
accumulate unduly. In Southern Mesopotamia the
rainfall is not inadequate, and combined with the
annual flooding from the Tigris and Euphrates
would be sufficient to sustain considerable vegeta-
tion, were it not for the physical peculiarities of
fine silt. Here, in fact, we have country which

Fig. 14. — Salt Patch in Lower Mesopotamia. {Photo : V. H. W. Dowson.)

Fig. 15. — Salt-loving Vegetation on the Plain of Jericho, Palestine.
{Photo : P. A. Buxton.)

THE SOIL AND WATERCOURSES 47

is desert, not because of its climate, but because
of the physical characters of its soil.

The fact that smooth, hard deserts of silt or
clay or loess support a very small fauna is partly
due to the small number of plants occurring, but
also to the fact that natural shelter from sun,
drought, wind, and light is difficult to obtain.
Even species which are capable of excavating
burrows for themselves are liable to be drowned
out by every storm of rain.

Very large areas of the Great Palsearctic Desert
are composed of mixed stone and earth. This
type of desert consists of varying proportions of
stones, large and small, lying on and in clay or loess
or fine earth of other kinds (Fig. 26). This mixed soil
carries a relatively rich flora, if cHmatic conditions
are not imfavourable. The finer element in the
soil supports the flowers which it would naturally
support if it occurred alone, and the presence of
stones which hinder evaporation and by that means
tend to conserve soil moisture, enables other plants
to exist. In fact the mixed type of soil results in
a rather varied flora, and this in turn increases
the fauna. Apart altogether from their depen-
dence on the plants, animals are more numerous
in stony deserts because they find shelter from the
cHmate under the stones. This point will be dis-
cussed later (pages 100-101 ). Stony desert, and semi-
desert, is very widely distributed in the Palsearctic
region, for instance in the Northern Sahara, the
south of Sinai and Palestine, and large areas in
Persia, Afghanistan, and Baluchistan.

48 ANIMAL LIFE IN DESERTS

Gravel desert, a type which consists apparently
of pebbles with very little fine soil to fill up the
interstices, has been described by Blatter and Hal-
berg in Rajputana, and by Thomas on the edge of
the Libyan Desert, north-west of Cairo. The inter-
vals between the individual pebbles allow the
immediate escape of any rain which falls ; on the
other hand, the surface of gravel desert is not
liable to be moved by the wind. Gravel desert,
as might be expected, supports a very poor flora :
Thomas says that " standing in most places it is
impossible to see a single plant anywhere around
one. ... At a period when the annuals have
disappeared I have traversed several miles on
patrols, without seeing a single plant." Though
he studied his area during and after the spring
rains he was only able to identify eight flowering
plants in the gravel desert.

Outcrops of bare rock may occur in deserts of
almost any type. Small areas of rock present
intense difficulties to colonization by plants or
animals : in any cHmate the plants growing on
rock surface are rare, because soil is only found in
small pockets (Fig. 18), and because nearly all the
rain received runs off the rock at once : in deserts
the difficulties are intensified. Larger areas of
rock are less hostile to flora and fauna because they
nearly always include patches of soil and little
islands of plants. In most large areas of rock,
caves occur, with their speciaUzed fauna and rela-
tively stable climate. A reference to the animals
which are found in desert caves will be found on

Eigs. 16 and 17. — Hills of Salt Mud near the Mouth of R. Jordan, near
Jericho, Palestine. {Photo : P. A. Buxton.)

THE SOIL AND WATERCOURSES 49

page 104. In Fig. 18 I have illustrated a type
of rock desert in which strata of hard and soft
calcareous rock alternate. On the softer large
numbers of spring flowers grow : these valleys are
full of caves, both natural and artificial. Typical
birds in this type of country in Southern Palestine
are Rock Doves, Wheatears {Saxicola lugens and
others). Rock Partridge (Alectoris =Caccabis),
Ravens (Corvus ruficollis), and Tristram's Grackle
{Amydrus tristrami) : among mammals, Porcupines
and the Coney or Hyrax (Procavia).

The influence of watercourses upon desert life
is very much greater than might be supposed.
Many of them are temporary, fed by snow, or by
rain faUing on some distant mountain mass, and run
out into the desert plains, where they gradually
disappear owing to evaporation and seepage into
the soil. The length of such a river varies immensely
with the season : at the end of a period of drought
the whole bed may be dry (Figs. 19, 20, and 21) ;
after a period of heavy rain a torrent may be pro-
duced sufficient to flow several hundred miles down
a bed which has been dry for years. One of the
longest of these dry watercourses is the Wadi
Rummah, which rises near Medina in the highlands
of Western Arabia, and at one time crossed the
peninsula to discharge its waters into the Shatt al
Arab near Basra. It is more than a thousand miles
long, though its course is now blocked by large
areas of sand dunes and water never runs from
end to end of it. In some of these torrent-beds
bushes and other vegetation grow (Figs. 20 and 21) :

50 ANIMAL LIFE IN DESERTS

in others the floods are so violent, or the soil is so
unfriendly, that nothing grows (Fig. 19).

These apparently dry beds form Hnes along which
subterranean water drains, and in many of them
it may be found by sinking a weU to a depth of a
few feet. This subsoil water determines the pre-
sence of a relatively dense vegetation (Fig. 21),
consisting often of a fairly large number of species ;
these in turn provide food and shelter to very many
animals. The bed of the stream gives Hfe lavishly ;
as lavishly as it destroys it. A sudden heavy rain-
storm, such as is common in deserts (page 13),
falls, the water runs rapidly off the bare ground
and produces a devastating flood. Shakespear saw
such a flood as this in the Batin (lower part of
Wadi Rummah) in Central Arabia ; twenty minutes
of heavy rain converted the dry bed into a rushing
torrent 3 feet deep, 50 feet across. Such floods are
not rare in Arabia. Philby has suggested that the
desolation of the once populous Wadi Hanifa was
due to a great flood which obUterated the settle-
ments in the bed of the Wadi, and spared those
on the sloping ground around ; he records a flood
in Wadi Dawasir which filled weUs, and destroyed
a hamlet, and another which drowned 150 men,
450 camels, and thousands of sheep, if local report
is reliable. Palmer records a flood which destroyed
forty bedawin and their flocks in the Wadi Solaf
in Sinai, and doubtless examples might be multipUed.
Certain desert areas are traversed by great
perennial rivers, such as the Tigris and Euphrates,
the Nile, and the rivers of Transcaspia. In Lower

THE SOIL AND WATERCOURSES 51

Mesopotamia and the Nile Valley, and on the great
plain through which pass the Amu Dana (Oxus)
and Syr Daria (Jaxartes), plant and animal life
depend less on local rainfall than on the annual
flooding of the ground at the time when the river
is at its highest. The height to which the river
rises varies greatly from year to year, and depends
on precipitation and the melting of snow in far-
distant regions. The Nile is under partial control
and the height of its annual rise is more constant
than it would otherwise be : the Tigris is not under
control, and the Euphrates only to a very sHght
extent. It follows that in a year of exceptionally
high water great areas of Mesopotamia which would
otherwise be unflooded are inundated in March and
April and remain covered with water for several
months. This not only keeps the soil of the plain
moister than it would otherwise be in early summer,
but materially modifies the summer heats, and
appears to double or treble the number of insects
which are on the wing throughout the whole sum-
mer. On the other hand, this annual flooding of
a flat land is very unfavourable to the burrowing
animals and appears to limit the species of lizards
and small mammals very materially.

It is noteworthy that the majority of closed
drainage basins, from which there is no outlet to
the sea, are desert. This is probably due in the
main to the fact that in them salts accumulate,
until the increasing salinity of the area causes it
to become desert. Examples are the great basins
of Central China, Eastern Turkestan, and the Sahara,

52 ANIMAL LIFE IN DESERTS

into all of which rivers run from the surrounding
uplands without ever making a sheet of water in
the centre. Other closed basins, without outlet to
the ocean but with inland seas or lakes into which
they drain, are those of the Dead Sea and Jordan
Valley ; the Caspian with the Mugan Steppe and
the steppes of 'the Volga and Transcaspia ; the
Sea of Aral with the Oxus and Jaxartes Rivers
and the great plain of Russian Turkestan ; the
Shotts (Chotts) of Southern Algeria and Southern
Tunisia ; the Great Salt Lake in the State of Utah ;
Death Valley and the Salton Sea in California ;
and the Lake Eyre basin in Central Australia. All
of these areas are desert, and the Dead Sea, the
Caspian, the Sea of Aral, Death Valley, Salton
Lake, and Lake Eyre are all beneath mean sea-level.

Fig. 20. A Flood Chaxnkl near Jericho, dry except for a few

DAYS OR EVEN HOURS IN THE YEAR. {PhotO : P. A. Buxton.)

Fig. 21. — Bed of a Wadi at Biskra in the Algerian Sahara,
SHOWING Bushes of Oleander {Nerium) and Tamarisk {Tamarix).
{Photo : V. H. W. Dowson.)

CHAPTER III
THE FLORAL ENVIRONMENT

I shall discuss the vegetation of deserts, not as a
botanical problem, but because the plants are a
very important element in the environment of the
fauna. It will be appreciated that many of the
characteristics of desert plants which are of great
interest to the botanist, and to the study of which
notable contributions have been made, appear to
matter but Uttle to the zoologist, who is interested
not in the plants themselves, but in the plants
considered as a part of the surroundings of the desert
animals. It would be rash to say that such things
as the pitted stomata and highly concentrated sap
of plants growing in dry places do not affect the
fauna, but at any rate it is not at present apparent
that they do so. I have therefore omitted these
and a number of other points to which the botanists
have devoted attention.

It is impossible to draw up such a description of
desert scenery and vegetation as would be appHcable
to the deserts of aU the continents and both the
hemispheres. It is, however, true to say that the
prevaiHng tint for the greater part of the year is
that of the soil, for the plants grow so far from one

54 ANIMAL LIFE IN DESERTS

another that they do not colour the landscape, except
for a short period after rain has fallen. In most
deserts bushes are rare and tend to become con-
spicuous features of the scenery, if they are present :
trees are so rare that they are regarded with venera-
tion by desert-dwelling races in more than one part
of the world. At certain spots in the desert water
is available in relatively large quantities : such spots
are oases, and are characterized by a dense growth
of vegetation, often consisting of plants which do
not and cannot grow in the surrounding desert, and
which are not found outside the oasis, until a second
oasis is reached. This growth of vegetation provides
food for a number of animals, many of which are
specially dependent on one of the oasis plants, or
for some other reason unable to live in the surround-
ing desert. The edge of an oasis is usually extremely
sharply defined : the plants of the oasis grow up
to the edge of the area which has the abundant water
supply, and there they stop abruptly. Fig. 23
illustrates this admirably.^ On the left is a dense
growth of poplar, fig, apricot, bramble, and many
other wild and cultivated plants, dependent on a
perennial spring in the bottom of a " wadi " : on the
right, a yard or two away, is the " wilderness of
Judaea," with no living plants except Atriplex
halimus, and not many of that. The photograph
was taken in July, after the spring annuals had died :
their dried remains may still be seen. Fig. 22 gives
a general view of the same country.

Very few natural oases exist, and many of them
1 See also Fig, 10, opposite p. 42.

Fig. 22. — Wilderness or Jud^a, between Jerusalem and Jericho.
{Photo : V. H. W. Dowson.)

Fig. 23. — Wadi Kelt, Wilderness of Jud^a, Palestine. On the

LEFT ARE VARIOUS TreES AND BuSHES ; ON THE RIGHT IS THE BARREN

wilderness. {Photo : P. A. Buxton.)

THE FLORAL ENVIRONMENT 55

are only small thickets near such rivers as the Tigris
and Zarafshan, which flow through deserts. Nearly
all the larger natural oases have long ago been
totally ruined by man, who has destroyed the
characteristic and very local flora and fauna, planted
carrots and cabbages and dates (Figs. 10, 12), and
introduced along with them the common garden
weeds and the common garden insect pests, so that
to a naturaUst a " well-developed " oasis is one of
the most uninteresting sights in the world. The
water which turns a given part of the desert into an
oasis may come from any source, from springs, or
seepage from a water-bearing stratum, from a passing
river, or even from an artificial canal or artesian well.
The deserts of the Old World are great plains,
and the vegetation is siu*prisingly monotonous and
uniform over immense areas. Many genera and
species of plants range from the western Hmits of
the Sahara, or even from the barren parts of the
Azores, Canary and Cape Verde Islands, eastwards
to Sind and Turkestan. Conspicuous examples are
the Colocynth {CitruUus colocynthus), the Saltbushes
(Suceda and Salsola), and members of the genus
Zizyphus (Fig. 25) ; very many others might be
mentioned which are distributed over the greater
part of the vast area. The uniformity of surface
and of vegetation, which is so characteristic of the
Old World deserts, is much less observable in
America. MacDougal states that he found only
thirteen species of flowering plants during a month's
trip in the Libyan Desert : twelve of the thirteen
belonged to very widely distributed species, and he

56 ANIMAL LIFE IN DESERTS

contrasts this with the fact that " many dozens of
species are known from places in American deserts
no larger than an ordinary farm, in single canons,
or on one slope of unique environic combinations."
He suggests that the reason for this lies in the
comparative newness of the American deserts, which
consist of relatively small plains and steep mountains.
The environment is varied and the plants vary with
it. In the course of ages these deserts will undergo
a process of base-levelling, and will perhaps come to
resemble the immense desert plains of the Sahara,
Mesopotamia, and Transcaspia. By that time the
conditions will be so uniform, and have altered so
profoundly from those now prevailing in America,
that very many species wiU have ceased to exist.
The relatively unspecialized types, which have not
adapted themselves too closely to their environment,
will have spread widely and come to occupy vast
areas.

The plants which are found in deserts belong to
special genera and species which are so modified in
structxu*e, and in their manner of performing their
vital functions, that they can support life under very
unfavourable conditions. These modifications are
so great and so fundamental that the transfer of a
desert plant to a less severe environment, or of a
seaboard plant to the Arizona Desert, was always
followed by the death of the plant, in certain of
MacDougal's experiments ; on the other hand, the
transfer of plants to environments which were
strange to them, but were not desert, resulted in
quite a number of survivals.

THE FLORAL ENVIRONMENT 57

We have already seen that the rigours of a desert
climate abate in many places for a short season
every year. Plant life in deserts has suited itself
to the cHmatic conditions in many ways, of which
three are the most important. During the short
period which follows the rain annuals are common.
At the same season a group of perennial plants
which persist through the dry months dormant
underground produces its leaves and flowers. The
third principal group of desert plants consists of
perennials the structure of whose aerial parts is so
profoundly modified that they can continue their
vital functions throughout the year. We shall now
examine each of these groups more closely. The
first group, the annuals, is extremely conspicuous
after rain, so much so that for the moment the
desert is no desert, and the perennials, at other
seasons so conspicuous, cease to attract our notice.
The seeds of the annuals have survived a dry period
of months or years and have resisted terrific heat
and desiccation, but the stems, leaves, and flowers
are not anatomically modified for life in dry places.
The annual plants appear shortly after a fall of rain,
carpet the ground to a greater or lesser extent,
blossom in an incredibly short time, and then wither
rapidly when the soil and the air become dry.
Figs. 24 and 25, taken in the plain of Jericho in
February and June, show this. The spaniel dog
illustrates the depth and thickness of the spring
annuals. This ephemeral vegetation depends directly
upon the rainfall, and on it in turn depend a large
number of forms of animal life. In some parts of

58 ANIMAL LIFE IN DESERTS

the deserts of America there are two rainfalls : that
which occurs in December and January is followed
by crops of flowers of winter annuals: as soon as
the cold weather is passed : these then dry up and
perish. The summer rains come and soak the ground,
but the seeds of the winter annuals do not germinate ;
instead, there comes up a crop of summer annuals
which ripen seed soon after midsummer ; this seed
lies dormant all through the cold weather, even
though it is saturated by the winter rains. Whether
the desert has one rainy season or two these annual
plants add very greatly to the number of species
and of individual plants occurring in an area ; in
fact, a richness of flora is produced which for the
moment far exceeds the inroads made upon it by
the larger herbivorous animals : their number is
Umited by their abiUty to exist through the long
dry seasons. The smaller forms of animal Hfe, for
instance, the insects, increase in numbers enormously
as the annual vegetation grows, and Uke it rest in
various ways for the rest of the year.

The second large biological group contains plants
which exist beneath the ground during the dry
months in a dormant condition, and which produce
leaves, stems, and flowers after rain has fallen. The
perennial part of the plant is a bulb, corm, tuber, or
fleshy root. It is essentially an organ for storing
food, and it is by drawing upon these reserves that
the plant is able to respond rapidly to rainfall and
send up its flowers and leaves : there is no occasion
for the storage of water, for these plants are active
only at a season when water is abundant. Plants

THE FLORAL ENVIRONMENT 59

of this group are particularly common in the semi-
deserts and deserts of Palestine, Sinai, Persia, and
indeed in most parts of the Great Palsearctic Desert.
Many of them belong to the Lily, Amaryllis, and
Iris famiUes, and famihar examples are colchicum,
squills (the broad leaves of which are shown on the
right in Fig. 26), tuHps, asphodels, onions, and stars
of Bethlehem. Their reserves of food are stored in
different parts of the plant : in Stars of Bethlehem
(Ornithogallum), onion (Alhum), and others, in
closely packed leaf -bases constituting a bulb ; in
iris, crocus, etc., in swollen subterranean stems
(corms) ; and in the roots in asphodels and others.

The third important group in the flora contains
those perennial forms which are so specialized that
they can exist above ground and perform their vital
functions at all seasons. To this end they are
modified in many remarkable ways ; roughly speak-
ing, the modifications fall within two groups, those
which tend to reduce the loss of water from the
surface of the plant, and those which tend to preserve
a store of water in the body of the plant. Many
forms exhibit both types of modification. In the
first group of adjustments to environment we find
that the leaves are small or absent, or only produced
after rain when the soil and the air are relatively
damp ; at such times loss of water from the surface
of the leaf is of less importance than during the dry
season. In those plants in which the leaves are
greatly reduced or absent the twigs and stems are
green ; it is the chlorophyl in these organs which
carries on the function of starch manufacture, a

60 ANIMAL LIFE IN DESERTS

function performed in ordinary plants by chlorophyl
in the leaves. When leaves are present they are
often extremely tough and leathery ; the cuticle, in
particular, is greatly thickened and the surface is
protected in many species either with wax or with
resins, or with incrusted salts, or with densely
matted hairs : it is beHeved that all these modifica-
tions, which occur in desert plants of the most
widely different famiUes, enable the plant still
further to reduce the amount of water which it
loses by transpiration. In all deserts a certain
proportion of the plants become succulent, that is
to say, develop the capacity of storing a considerable
quantity of water. Succulence is not only a char-
acteristic of desert plants, but of those growing in
any environment in which the available moisture
is limited: some succulents, for instance, grow on
salt-marshes, others on rock surfaces and roofs and
walls, even in damp cHmates. Most of the desert
succulents are found in areas with a rainfall which is
sHght but fairly regular, and they are not generally
found in intense deserts and in cUmates without any
regular precipitation. They are developed in an
apparently capricious manner in certain deserts and
not in others. For instance, the cacti, nearly all
of which are succulent, some of them extremely so,
are numerous both as species and as individuals in
the deserts of the southern United States and of
Mexico. In the arid parts of South Africa their
place is taken by plants of the Spurge family
(Euphorbiaceae), and some of these plants so closely
resemble the cacti of the New World that they can

THE FLORAL ENVIRONMENT 61

barely be distinguished from them until they flower.
This is an example of convergence, the production of
very similar structures by plants which are not at
all related to one another, as a response to similar
environmental influences. On the other hand, succu-
lents are rare in the Great Palaearctic Desert, speaking
generally, and the cause is unknown, for in many
places the conditions of weather and soil are such
as appear to favour succulents in American and other
deserts. The only noteworthy exception is the salt
parts of the Great Palsearctic Desert : in these such
genera occur as are familiar in saltings in many
parts of the world.

Nearly every part of the plant body, but most
commonly stems and leaves, may be used for the
storage of water. In the Cactus family, for instance,
the stem is greatly thickened and often nearly
globular : it is used for the storage of water, and
MacDougal states that tree cactuses may contain as
much as a thousand gallons. Succulence of the stem
occurs also in spurges and many other families : in
Southern Mexico there is an Ipomsea, a plant closely
alHed to the convolvulus, which has a soft thick
trunk containing water, and Beaucarnea, a relative
of the Yuccas, is so charged with water that its
trunk is 7 or 8 feet in diameter, though the tree
itself is not above 25 feet high. An example of
a plant with succulent leaves, Calotropis procera
(Asclepiadacese) is shown in Fig. 27.

It will be seen that there is a most interesting
contrast between the second and third groups of
desert plants. Members of the second group have

62 ANIMAL LIFE IN DESERTS

little need for a reserve of water, for they are only-
active after rain when the soil is damp ; they store
food in the form of starch and allied substances,
so that when the rain is received they can at once pro-
duce active growth. Members of the third group are
active at all seasons ; they therefore are able to
manufacture their own food as they need it : many
of them possess storage organs, but they store water
not food.

The sap of many succulent plants is saUne or
bitter : this appears to protect the plant from
animals in many instances, but it does not follow
that the primary function of the bitterness is
protective. In certain instances it is known that
the water accumulated by succulent plants is of use
to animals ; for instance, the donkey can be watered
with the juice of the giant cactus (Cereus giganteus),
which is too bitter for man's use, and the barrel
cactus (Echinocactus) furnishes several pints of fluid
which even man drinks readily.

Thorniness is possibly more characteristic of the
third group of desert plants than succulence : it is
a character common to the plants of deserts in all
countries, and of every type of desert, and it is
exhibited by herbs and bushes belonging to a very
great number of different natural orders. It is
found on the most varied parts of the plant body ;
the stem may be thorny, and the leaves may be
covered with thorns, or may themselves be trans-
formed into thorns ; the fruits also may be thorny.
It is believed by many that the thorns protect the
plant against herbivorous animals. This point will

THE FLORAL ENVIRONMENT 63

be considered in greater detail in the chapter which
considers the relationships between plants and
animals in the desert. Here I shall only say that
the view that thorns are defensive is difficult to
maintain, except in a few special instances. On the
contrary, it appears probable that the thorniness of
the plants that grow in deserts is due rather to
physical than biological influences. It is known
that if a plant is grown in a dry atmosphere it
produces a relative increase of various hard sub-
stances at the expense of its starches and plastic
materials ; it is also known that cultivation in a
damp atmosphere retards the development of thorns
in seedlings. It is therefore possible that the
thorniness of desert plants is a purely physical or
chemical phenomenon, and that any protection that
the plant derives from it is purely incidental.

CHAPTER IV

ANIMALS AND THE PHYSICAL ENVIRON-
MENT : GENERAL RELATIONSHIPS

General Relationships

We have considered the surroundings in which
the desert animals live, and seen that the chmate
and other physical factors are generally unfavourable
to ordinary animal life. We shall now study some
of the adaptations which enable the animals to
overcome the obstacles of their physicietl environment,
and to draw sustenance from the specialized flora of
the desert.

Every element of the desert climate is liable to
rapid fluctuations, which are often quite irregular :
and in many desert places the great heat and
drought, and violent winds and other climatic factors,
all combine during the summer to be most hostile
to the flora and faima.

The habit of aestivation in plants has been already
referred to (pages 57-59). A similar habit is common
in the invertebrate animals of desert faunas. In
the present state of knowledge we can only attribute
it in broad terms to the extreme hostility of the
summer climate ; but it may well be that as we
study the effects of varying temperature, or humidity,

ANIMALS— PHYSICAL ENVIRONMENT 65

or other conditions, upon particular species, our
knowledge will become more accurate. We shall
perhaps find that in the case of one creature the
cessation of activity during summer is induced by a
mean temperature above a certain degree, or in
another by a minimum daily humidity below a
certain percentage. Until the particular effect of
altered cUmatic conditions upon selected species of
animals has been studied we cannot do more than
record the facts, which are that the great majority
of the invertebrata in deserts undergo periods of
dormancy either in winter or in summer, or both.

In Mesopotamia it is easy to notice that insects
are commonest after the winter rains, during the
temperate spring and early summer. From April
to June nearly aU insect life is fully active, and its
activity coincides with and follows the rapid growth
and blossoming of the spring vegetation. During
the hot dry months of summer the insects are not
in evidence ; as the weather becomes cooler there
is a distinct, though less evident, increase in the
number of insects on the wing. Figs. 28 to 30 are
compiled from collections made at Amara, R. Tigris,
by Capt. W. E. Evans, R.A.M.C., and myseK.
, It would scarcely be extravagant to claim that our
collections are a fair random sample of the fauna
of Amara at all seasons. We had few distractions
and were deeply interested in entomology ; we each
resided in Amara for almost exactly one year ; we
felt that we were in an imknown land and there-
fore collected everything, even species which were
common, in long series when we could; we could

ANIMAL LIFE IN DESERTS

identify none of our captures and therefore did not
discriminate ; and we generally worked independ-
ently, in different parts of the area round Amara.
Fig. 28 shows the monthly occurrence and relative
frequency of certain famiUes of Orthoptera. It wiU
be seen that the Praying Mantis family was repre-
sented by most species in April and September;

ill fV

VJ VII VIII IX

XI XII

Short-horned Grasshoppers. — Crickets.

Mantis family Long-horned Grasshoppers.

Fig. 28 — Number of Species of Certain Families of Orthoptera

PRESENT month BY MONTH IN COLLECTIONS MADE AT AmAJIA, LoWER

Mesopotamia, by W. E. Evans and the Author. The Months

ARE SHOWN by RoMAN FiQURES, THE NUMBER, OF SpECIES] OCCUR-
RING BY Arabic Figures.

the Long-horned Grasshopper family in May and
October ; and that of the Short-horned Grasshoppers
in June and October. The Crickets, which are
nocturnal and shelter by day under logs and in
holes and cracks in the groimd, do not show this
seasonal incidence ; the conditions to which they
are exposed are different and they react differently
to them. The Hymenoptera (Fig. 29) show similar

ANIMALS— PHYSICAL ENVIRONMENT 67

curves ; the Fossors are most abundant in June and
September; the bees in July and September.
The Ruby Wasps (Chrysids) and Wasps (Vespids)
were represented by so few species that curves
have not been constructed from them, but the
curve for all four families shows maxima in June
and September. Even the moths comply in the
main with this rule, which could hardly be expected,
as the majority of them are nocturnal, and shelter

XII I II ill IV V VI VII VIII IX X XI XH

Four families. Fossors

Bees.

Fig. 29. — Graph similar to Fig. 28, showing the Monthly Prevalence
OF THE Fossors (" Solitary Wasps "), Bees, and " Four Families "
OF Hymenoptera (i.e. Fossors, True Wasps, Bees, and Ruby

Wasps) at Amara.

by day in places in which they must be protected
from the great heat and low humidity. The curves
in Fig. 30 all reach maxima in May or June, and in
September.

Certain groups of insects showed a different
seasonal prevalence, amongst others some of the
butterflies, of which very few species were found at
Amara. The Clouded Yellow {Colias croceus =
edusa), Common White {Pieris rapce), and three Blues
(Zizera karsandra, Tarucus halcanica, and T. mediter-

ANIMAL LIFE IN DESERTS

ranece) were all on the wing from March to June and
again from September to November. A few indi-
viduals of several of these species were taken in the
intervening hot months, but these species were rare
at that season and clearly fall into the same group
as the Orthoptera, Moths, and Hymenoptera (Figs.
28 to 30). Three species, however, had totally
different seasons. One " Blue " (Chilades gatba)

XII I II III IV V VI VII VIII IX X XI XII

■All families. Pyrales Noctuge.

Fig. 30. — Graph similar to Fig. 28, showing the Monthly Prevalence
OP Pyrale and of Noctuid Moths and of all Families of Moths
EXCEPT Pterophorina, Tortricina, and Tincina.

was abundant from June to August and was not
taken at other seasons, though its food plant was
always abundant and was in leaf all the summer and
autumn ; the " Skipper " Parnara matthias was
only taken from June to November ; and the
common salmon-coloured Teracolus fausta from July
to December.

The apparent absence of this species in spring and
early summer may be due to one of two causes.
The Caper bush (Capparis spinosa), its food plant,

ANIMALS— PHYSICAL ENVIRONMENT 69

is bare of leaves till the warm weather is well
advanced, and it is possible that the species Hes
dormant through the spring as egg, or resting larva,
or pupa, until the Caper bush is in fuU leaf. On
the other hand, it is possible that even the mild
winter of Mesopotamia is fatal to T. fausta in all
stages, and that it recolonizes this country every
spring by immigration from lands with warmer
winters ; in Palestine it seems extremely probable
that this species dies out every winter, and recolonizes
the land every spring.

It is convenient to mention here another Pierine
butterfly which eats Caper, the species known as
Belenois mesentina, although it was apparently
absent from Amara. It is a species which often
occurs in great numbers in very hot places, even in
the hottest weather : for instance, along the North-
West Frontier of India it is common from May to
October, a season during which the other butterflies
are scarce or not on the wing at all. It has an
extremely wide distribution, from tropical Africa to
India, and is by no means confined to deserts. This
wide distribution is possibly due to its ability to
continue active life at a time of year when heat
and dryness have caused most butterflies to cease
from flying, and this activity in the height of summer
may in turn be due to the fact that the Caper is
one of the not very numerous plants in full leaf at
that season.

It must be admitted that this study of the number
of species of insects on the wing in various months
is liable to one very grave criticism. Each group

70 ANIMAL LIFE IN DESERTS

of insects, in fact each species, finds this or that
month favourable to it for a different reason. The
mantises may be influenced by an abundance of
other insects on which they prey. The bees or
wasps may, for all we know to the contrary, time
their emergence more by the flowering season of
certain plants than directly by any cUmatological
event. The moths may fly at midsummer, not
because midsummer conditions suit them particu-
larly, but because several months before there was
abundance of herbage for their larvae. In fact,
Figs. 28 to 30 represent facts which are the result
of the action of very many factors : they cannot be
used as a basis of a theory. If we wish to interpret
the abundance of insects in a certain month, we
must take individual species of insects and study
their reactions to altered temperature, humidity,
food, soil, moisture, etc. We are not justified in
taking such curves as Figs. 28 to 30 and comparing
them without further analysis with the meteoro-
logical statistics, or the season of greatest plant
growth.

In the British Isles we are accustomed to think
that the warmer the temperature to which insects
are exposed, the more quickly do they go through
the various stages of their Hfe-history. This is
clearly a fallacy, because in Mesopotamia in many
different families of insects active life is in abeyance
during the hottest months. We can at present only
guess at the cause ; it is probable that heat and
humidity interact in such a way that neither factor
can be considered separately : a certain high

ANIMALS— PHYSICAL ENVIRONMENT 71

temperature is optimum for the development of a
certain insect only when the humidity is about a cer-
tain figure ; if the humidity is much below that figure
the temperature may be unfavourable or even fatal.

The curves in Figs. 28 to 30 show clearly that the
cessation of active Hfe in summer is less than that
in winter. One is accustomed to associate the
summer of Mesopotamia with fierce heat, acute
discomfort and the sudden death of Europeans who
were unable to avoid active work in the middle of
the day : apparently to the adult insect the summer
is less unfavourable than the winter, for it will be
seen that January provides far fewer winged insects
than July or August. Our conclusion, then, is
this : that aestivation and hibernation are common
phenomena among desert insects ; until we have
accumulated a mass of detailed analysis we must
accept it that these phenomena are, in a general
way, due to the climate in summer and winter being
unfavourable.

Ants, as Wheeler has shown, adapt themselves to
the desert seasons in several ways. In more ordinary
surroundings some ants are insect-eaters, but very
many Uve upon plant juices which they obtain either
directly or from Plant-lice (Aphidse) and Scale
insects (Coccidse) : in deserts they have to contend
against periods of drought. Some of them therefore
become extremely active predators, ranging far and
wide and running with great rapidity. Many others
collect seeds and pieces of dried plants, and depend
upon this harvest for food and moisture during the
summer. Others, again, collect plant juices, and

72 ANIMAL LIFE IN DESERTS

the secretions of Plant-lice during the season of
active growth which follows rain, and store these
fluids in the stomachs of certain specialized " worker "
ants ; these become enormously distended with
fluids, and are known as honey-pot ants, and from
them moisture is obtained during the dry period.
There are several genera (Camponotus, Myrmeco-
cystus, Melophorus) in which this habit has been
developed, and they are found both in the American
and Australian deserts.

It is natural that, just as the insects are most
numerous in the clement spring and temperate
autumn, so they are much more numerous in a
season following good spring rains and a normal
flood than in a year in which moisture and therefore
annual flowers have been deficient. In this connec-
tion the enormous variations from the normal which
characterize the annual rainfall of deserts (pages 11-
13) will be remembered. If the regular winter rains
are deficient the annual plants and the butterflies,
bees, and other insects are scarce as regards indivi-
duals ; apparently also certain species are entirely
absent, at any rate they are so rare that they are
not detected. The possibility that insects and plants
can " carry over " an unfavourable period not of
months but of years requires investigation, but
there is a good deal of evidence to suggest that it
may indeed be so. For instance, Hartert was in
the country south of Biskra, Algerian Sahara, in
1908 and 1909 : he noticed white butterflies very
rarely between Biskra and Borj Saada, and none
between Borj Saada and Tuggurt. In 1912, after

ANIMALS— PHYSICAL ENVIRONMENT 73

good winter rains, he travelled along the same road,
at the same season. He saw dozens of white
butterflies between Biskra and Borj Saada, and
hundreds of Melitaea and Euchloe between that place
and Tuggurt.

Spencer's observations upon the small mammals
and other creatures of Central Australia, and the
effect upon them of " good " and " bad " years, are
extremely interesting. After the wet season the
reproduction of the small rodents and marsupials
is at its height ; the succeeding drought kills a very
large number of them, especially the immature
individuals, and the few survivors attain maturity
without attaining the dimensions of individuals
reared under more favourable conditions ; for
instance, the adult males of the marsupial Phascogale
cristicauda may vary in length from 136 to 220
millimetres, and females carrying young from 125 to
170 millimetres. A succession of dry years not only
greatly reduces the numbers of small mammals, but
also reduces their powers of reproduction. Thus
the small, mouse-like marsupial Sminthopsis crassi-
caudata, which has typically ten nipples, produces
ten young at a birth in seasons of plenty, and not
more than four or five in seasons of scarcity. " If
the drought be abnormally prolonged then even the
hardiest animals will suffer, and the fauna wiU be
so reduced that it may take some time before
increased fertility on the part of the survivors and
the influx of immigrants from the broad belt of land
enclosing the central region will make good the
deficiency " (Spencer).

74 ANIMAL LIFE IN DESERTS

The effects of good rain upon bird life is illustrated
by Ticehurst's observation that the White-cheeked
Bulbul {Pycnonotus I. leucotis) of Sind, which normally
breeds in March and April, breeds again in Sep-
tember in years in which much rain has fallen.
The fact that this bird is a denizen rather of thickets
and gardens than of the bare desert does not render
it unsuitable for inclusion in our study of the biology
of deserts, for the conditions of cUmate and the
variations between " good " and " bad " years are
essentially the same in the desert as in the oasis.
It seems that this observation and Spencer's upon
the small marsupials are best included here rather
than in the section which deals expressly with water,
because quite clearly the increased reproduction of
bird or marsupial is not to be ascribed directly to the
rainfall but to some much more general effect of
the rainfall upon vegetation, insects, etc., and so
indirectly upon the larger creatures.

The present is a convenient place for considering
a remarkable type of small mammal which has
been evolved repeatedly in deserts and semi-deserts,
and not in any other environment : as we are
ignorant of the causes which have contributed to
the production of this type it appears best to group
it with other general relationships with the physical
environment. The mammalian type to which I
refer is most familiar to us in the Jerboa (Fig. 31).
This is a rodent about the size of a rat, provided
with short f ore-Umbs, which are not remarkable, and
excessively long hind-legs and long, narrow feet ;
the toes are reduced in number to two ; the tail

ANIMALS— PHYSICAL ENVIRONMENT 75

is very long, covered with short hairs, and bearing
at its tip a large tuft. The short fore-Umbs are
used for burrowing, holding food, and apparently
also for lifting water to the mouth (page 90) :
the length of the hind-limbs is correlated with the
habit of progressing by leaping and not by running,
and it is possible that they serve also to give the
Jerboa and the animals which resemble it an in-

Fig. 31. Hairy-footed Jerboa {Jaculus jaculus) from Egypt.

Notice the long hind-legs with reduced number of toes, and the long tail^with a terminal
tuft of hair, and the biped attitude. (Draum from life by Miss A. M. Gayton.)

creased power of observing the approach of enemies
on the bare ground. The speed which a Jerboa
can attain by jumping, and the great irregularity
of its movements, undoubtedly make it extremely
difficult to capture, a fact which can be verified if
you liberate a Jerboa in the confined space of a
room and endeavour to catch it in a butterfly net.
The Jerboas (Dipus and Jaculus) belong to the
Dipodidse, a family of Rodentia of which all the

ANIMAL LIFE IN DESERTS

members are modified in the same direction as the
Jerboa, though not all to the same extent. In
AUactaga, for instance, five toes are present on the
hind-foot, though two are vestigial ; in Scarturus
the first digit is absent, and the fifth vestigial ; in
Dipus and Jaculus only three toes are present,
and the two which are lacking are not represented
by any vestige externally (Fig. 32).

Fig. 32. — UNDER'SURrACE or Right Foot of Allactaga indica {A), Scar-
turus tetradactyla {B), and Jaculus jaculus (C).
{After R. I. Pocock.)

These genera are characteristic of the Great
Palaearctic Desert and of the steppes on its fringe ;
the closely related Zapus is American, and is inter-
esting because it is intermediate in habit and
anatomy between the ordinary running quadruped
mice and the biped jumping Jerboas. In another

ANIMALS— PHYSICAL ENVIRONMENT 77

family of rodents, the Muridae, the same modifica-
tion of form may be seen in desert species belonging
to two of the sub-famiUes. Of the first, the Ger-
billinae, or Gerbils ^ (Fig. 33), no member has be-
come completely biped, but nearly all the genera
and species show some lengthening of the hind-leg
and hind-foot and tend to progress at times by
running, at others by leaping. The species figured

Fig. 33. — East African Gerbil {Taterona mcina) from East Africa.

This animal is typical of a very large number of species, most of which are found in various
parts of the Great Palaearctic Desert. (Drawn from life by Miss A. M. Gayton,)

(Taterona vicina) shows these characteristics well,
and is drawn from life in a characteristic biped
attitude. Other Gerbils (e.g. Meriones) are more
rat-Hke in form and in habit. In the second sub-
family, the Murinse or True Mice, occur Conilurus
and Notomys in the Australian deserts, exhibiting
various stages in the lengthening of legs and feet

^Examples are Meriones (pages 92, 130, etc.), Gerbillus
(page 138), and Dipodillus (pages 103, 127).

78 ANIMAL LIFE IN DESERTS

and the assumption of the biped habit. In the
deserts of the southern part of North America
animals resembling Jerboas have been evolved
from yet another family of rodents, the Hetero-
myidae.

The rodents which have already been mentioned
all belong to the section Myomorpha ; in another
section, the Hystricomorpha, and not closely related
to the forms which have been considered, is the
Cape Jumping Hare (Pedetes). This animal is
much larger than any Jerboa, but resembles that
animal in its long hind-legs and long tail : it feeds
on all fours, but when it is pursued it escapes by
prodigious leaps. It lives in arid and desert places
in Africa from Mozambique southwards.

It is surprising to find similar " Jerboa-like "
animals among the totally imrelated marsupials :
good examples are Phascogale Hillieri and Ante-
chinomys. The last lives in Central Australia in
sandy plains among tussocks of grass in the same
environment as the rodents Conilurus and Mus
gouldi. The Antechinomys and Conilurus are Jer*
boa-like, progress by jumping, and show remarkable
general similarity in form ; the Mus, which is equally
common, and apparently quite as successful in the
business of life, is an ordinary mouse, and pro-
gresses by running : it is difficult to see why the
jumping habit has been evolved in the Conilurus
and Antechinomys unless, as Spencer suggests, the
resultant irregularity in movement tends to baffle
small hawks chasing them. Conilm*us is an ex-
tremely abundant rodent ; Antechinomys, which

ANIMALS— PHYSICAL ENVIRONMENT 79

so closely resembles it in habits and shape, is very-
rare, possibly because it is an insect-eater (page 83).
Every one of these small Jerboa-like creatm*es
exhibits the coloration typical of so many desert
animals (page 141), the sandy, unicolorous upper
surface, and white belly.

For the following tables I am indebted to the
kindness of Mr. O. Thomas, F.R.S., of the British
Museum (Natural History). The first makes clear
the relationships of the forms of which I have
been speaking ; it shows that animals outwardly
resembling the Jerboa have been evolved on a
number of different occasions, apparently as a
response to the conditions of life in a desert, and
that in each continent the Jerboa-like animal has
been produced from a different family or sub-
family.

Order.

Section.

Family.

Sub-family.

Genus.

Habitat.

Rodentia

Myomorpha

DlpodldsB

Dlpodlnae

AUactaga

Dipua

Jaculus

Great Pate-
arctic Des-
ert

Zapodinse

Zapus

America

»>

Murldse

MurinsB

Conilunis
Notomys

Australia

GerbllUnsa

Gerbillus
Meriones
DipodiUus

Great Pate-
arctic Des-
ert

•

•>

Heteromyid»

Dlpodomys
Perognathua

America

>»

Hystrlcomorpha

PedetldsB

Pedetes

S. Africa

MareupiaUa .

Polyprotodontla

DaayuridsB

DasyurlnsB

Antechlnomys
Phascogale

Australia

The second table shows at a glance the number
of toes present in these Jerboa-Hke animals, and
emphasizes the fact that a reduction in the number
of toes has repeatedly taken place. Five is of

ANIMAL LIFE IN DESERTS

course the full number of digits in either the fore-
or the hind-foot. " 4 and 1 " or " 3 and 2 " indi-
cate that 4 (or 3) normal digits are present and 1
(or 2) which is reduced in size. Toes are only
shown as " vestigial " when they are minute, and
probably not used : thus Perognathus has five
digits on the hand, of which one is small : on the
foot it has either three normal toes and two small
ones, or else (in another species) three normal toes,
one small and one vestigial. A zero in the " ves-
tigial " column indicates that no external trace of
digit can be found. In Dipus and Jaculus the
reduction has gone so far that two toes are not
even represented by a vestige.

Genus.

Dipus, Jaculus .

Scarturus

AUactaga

Gerbillus

Zapus

Perognathus, either

or
Conilurus
Notomys ...
Antechinomys
Phascogale hillieri
Pedetes .

Number of Toes.

Fore -foot.

4 &

Hind-foot.

Functional. Vestigial,

CHAPTER V

ANIMALS AND THE PHYSICAL
ENVIRONMENT (continued)

i. Water Supplies, ii. Fauna of Waters in Deserts, iii.
Heat and Relative Humidity, iv. Animals and Wind. v.
Relationships with Soil.

i. Water Supplies

I propose to marshal some of the available facts
which relate to the reaction of the desert animals
to drought, heat, wind, and other particular ele-
ments in the cHmate, and to deal first with the
means adopted by the animals for making the
most of a scanty and irregular water supply. In
many semi-deserts and in all deserts rain falls
at such rare intervals that life would be impos-
sible to any species directly and solely dependent
on it, but other sources of water are available,
and probably on the whole more important. Per-
haps the most obvious is the dew. Meteorological
records of dew-fall are scanty from all parts of the
world, and observation of dew-drinking by small
animals are very few. Atkinson, writing of his
experiences at Abu Kir in Egypt, remarks : " The
water supply of the numerous beetles inhabiting
the patches of baked clay in the coastal deserts

81 o

82 ANIMAL LIFE IN DESERTS

was a puzzle to the writer till it was noticed that
they drank drops of dew from the angles of dried-
up thorny plants."

Though lack of precise observation prevents us
from forming a clear idea of the importance of dew
to the fauna, it is probably considerable, at any
rate at certain seasons. A more constant source
of supply is the desert vegetation. Plants, however
dead they are, and however long they have been
exposed to the desert wind and sun, are not chemi-
cally dry, any more than hay or chaff are dry.
It has also been suggested that during digestion
by an animal a certain additional amount of water
may be elaborated as a by-product of the break-
down of the complex chemical bodies of which the
plant consists.

One can therefore understand that it is possible
for a seed-eating mammal or bird to exist for long
periods without eating succulent plants or drinking
the dew or obtaining water from any visible source,
and some of them can do this. I remember an
Egyptian Jerboa which was kept by a member of
my family as a pet. It was given no water and
lived for many months on crushed oats and bran ;
when it was offered apple or carrot or other moist
food it generally refused to eat it. That it could
not drink dew is certain because it Hved in a London
house. It is almost certain that many birds, in-
sects, and small mammals depend solely upon the
minute quantities of water to be found in seeds
and dead plants which have become completely
" air-dry."

ANIMALS— PHYSICAL ENVIRONMENT 83

It is reasonable to suppose that just as some
animals obtain their small requirements of water
from the plants they eat, so others obtain their
supply from the ants, grasshoppers, etc., which are
their staple food : such cases are probably few be-
cause animals which are dependent upon insects for
their food and drink are uncommon in aU deserts :
this applies not only to the order Insectivora but
also to insect-eating members of other orders.
This rarity is due in all probabiHty to the great
seasonal fluctuation which occurs in the number
of insects, and that in turn follows the enormous
variations in climate to which all deserts are sub-
ject. In the Great Palsearctic Desert I know of
no purely insectivorous ^ mammal, except the bats.
Of the food of such resident birds as the Desert
Warbler {Sylvia nana), which is probably a pure
insectivora, we have no accurate information. In
the Australian deserts the ants are a dominant
group : it appears that they are the staple food of
Myrmecobius, a marsupial ant-eater, which devours
them above ground, and of Notoryctes, the marsupial
mole, which lives beneath the surface.

Actual water-holes, springs, rivers, etc., provide
water to the creatures which live on their banks,
and to a number of others which come in from the
surrounding deserts to drink. Among them are
many birds, and bats, a few insects, and many
large terrestrial mammals.

^The hedgehogs which inhabit many parts of this area (e.g.
Hemiechinus auritus), though '* Insectivora " in the technical
sense, are not an exception to this statement, for they are by
no means exclusively eaters of insects.

84 ANIMAL LIFE IN DESERTS

Among birds which fly to water the most remark-
able are the Sandgrouse (Fig. 34). Sportsmen are
aware that-ithe various species of S andgrous e
(Pterocles and other gener a),jKh igtrt fiKabit nearly
J every part of th e Great Palsearc ticjesert water
hff at certain spots on the banks^ of rivers, at certain
' regular "EourS. There is good evidence that the
birds fly in from very many miles, and as the chosen
watering-place is often very circumscribed, immense
numbers of birds congregate there for a very short
period every day. Different species of Sandgrouse
water at different times of day, the majority in
the early morning, Lichtenstein's Sandgrouse before
sunrise, or even in the middle of the night when
there is moonUght. / Sandgrouse normally stand in
jW shallow water when drinking, and as their legs are
short their breasts become saturated with water.if
This is true of both sexes and happens at all sea-
sons. It is reasonable to suppose that from this
has developed their very remarkable manner of
supplying water to their chicks. Native hunters
have always asserted that they carry water to their
young in the hot, bare desert in their saturated
breast plumage. That this is correct has been
proved by Meade-Waldo, who has had many broods
of Sandgrouse (fifty-one of Pterocles alcatus, seven
of P. exustus, and three of P. arenarius) hatched in
his aviaries. /The young feed themselves on small
y, seeds^from the time of their emergence from the
i/" egg, and are attended by both parents. " The
male rubs his breast violently up and down on the
ground — a, motion quite distinct from dustmg, — and

ANIMALS— PHYSICAL ENVIRONMENT 85

when his feathers are awry gets into his drinking-
water and saturates the feathers of his underparts.
When soaked he goes through the motion of flying
away, nodding his head, etc. ; then, rememberng
his family is close by, he would run to the hen,
make a demonstration, when the young run out,
get under him, and suck the water from his breast
— ^the appearance being that of a mammal suckling
her young. / The young pass the feathers through
their bills, and keep changing places until the supply l^
becomes exhausted. Until the young can fly they
take water in no other way, and the cock gives it
to the young only.^"" (Meade- Waldo.) As soon as
the chicks can fly they cease entirely to drink from
the males' breast-feathers./ Sandgrouse in nature
breed at various dates, but one may say roughly
that they choose the hot weather. The following
are dates on which eggs of certain species have been
found in various places :

Western Pintailed

May

Spain.

Sandgrouse

Eastern Pintailed

May, June, July

Mesopo-

Sandgrouse

tamia

Spotted Sandgrouse

April, May, June,

Mesopo-

July

tamia

Little Pintailed

Throughout the

Punjab.

Sandgrouse

year, especially
March to July

Pallas' Sandgrouse

March to June

Central
Asia.

It seems that many young Sandgrouse are brought

86 ANIMAL LIFE IN DESERTS

into the world when the air is hot and dry, when
the desert soil is so hot that you cannot keep your
hand on it, and when the vegetation is parched
and the seeds on which they feed are already air-
dry. They run about, even during the hot hoiu-s,
near their parents but not sheltered by them, as
I have myseK seen at MandaH on the Perso-Mesopo-
tamian frontier in August. ^ As their only means
of maintaining a body temperature of about 100° F.
while they run in a dry atmosphere on desert,
the surface of which is 150° F. or higher, is by evapor-
ating water, it is not remarkable that special methods
have been evolved to bring water to them in their
waterless home. /What is remarkable is that the
other desert birds appear to Uve successfully without
watering their chicks at all. The Crested Larks
(Galerida cristata and G. thehloe) fly regularly to
water in the evening when water is available near
their haunts, though there is no evidence that this
habit is invariable or obHgatory ; the Stone Curlew
{(Edicnemus) and Coursers {Cursorius) do the same,
at any rate sometimes.

Ticehurst, writing of the birds of Sind, states that
the Trumpeter Bullfinch (Erythrospiza githagineus
crassirostris) drinks nearly every hour, and that
the Striated Bunting (Emheriza s. striolata) drinks
at frequent intervals during the day. So far as
we know none of the small desert birds give water
to their young by regurgitation, and certainly
none carry water in their breast-feathers. There
is a group of birds which seem to be entirely inde-
pendent of water, or rather to depend solely on

ANIMALS— PHYSICAL ENVIRONMENT 87

the water which they can obtain from dew, insects,
and the vegetation ; in this group fall the Houbara
Bustard (Chlamydotis undulata), the Chough Thrushes
(Podoces), the Larks Alsemon and Ammomanes, and
others.

Certain birds inhabit the fringe of deserts, but
seem to be prevented from penetrating them because
they cannot dispense with drinking. The need for
a drink of water is in these cases a Hmiting factor
in their distribution. An excellent example is the
Black Partridge (FrancoUnus vulgaris), an abundant
bird in the Mesopotamian plain. It is never found
more than a couple of hundred yards from water ;
it is a lover of thick scrub, but where scrub occurs
far from water the Black Partridge cannot be found.
In California a somewhat similar case occurs. The
Desert Quail {Lophortyx gambeli) wanders out into
the desert to forage, but its real home is] in the
scrub along the banks of ^the California River :
it requires to drink every morning and evening.

It is difficult to study the habits of bats. Cer-
tainly many desert-dweUing species visit water
regularly at the beginiy^ng of their evening flight,
but we have no reason to say that this is the custom
of desert bats in general.

Many wasps and other Hymenoptera make long
flights to drink, and crowd any spot at which they
can obtain water : some species require also mud
for nest-building. In Mesopotamia one often ob-
served the Oriental Hornet {Vespa orientalis) drink-
ing greedily in mess-rooms, and drowning itself
in drinking-cups : this had a considerable hygienic

88 ANIMAL LIFE IN DESERTS

importance, for the hornet was a filthy feeder and
was frequently loaded with bacteria derived from
the human intestine.

Among the large mammaHa there are many species
which drink, and drink freely, when an opportunity
is given them, but which are able to dispense with
drinking when it is necessary. They derive a
considerable quantity of water from the vegetation
which they eat, and one need hardly say that the
amount of vegetation, and of moisture in it, varies
very greatly with the season. Thus Doughty ob-
served in Arabia that " the camels now feeding in
the sappy rabbia (spring pasturage) were jezzin or
'not drinking.' In good spring years they are
in these diras almost two and a haK months jezzin,
and are not driven to the watering." Gregory
quotes very similar facts from Australia : he says
that in 1891 Tietkin marched 537 miles in thirty-four
days without watering his camels, and that PhilUpson
kept a herd without water in a sand-hill country
for two months. On the other hand, if very httle
grazing, or none at all, can be obtained and if camels
are doing hard work, their endurance is very much
less. Augieras speaks of sixteen days' march without
water in the Central Sahara as a severe trial to his
camels, and Haywood gives one to understand that
about eight days is near the camel's Hmit in mid-
summer in Tanezruft, a district of the Sahara which
at that season is entirely devoid of any grazing.
Camels not only possess this remarkable power of
abstaining from drinking for long periods, but they
are able to drink salt and bitter water which man

ANIMALS— PHYSICAL ENVIRONMENT 89

and horses cannot swallow ; when water is available
their consumption is low, about seven gallons daily
compared with the horse's thirty. Other large
creatures which are able to dispense with drinking,
but which drink when they have opportimity, are
the ostrich, the giraffe, the eland, and probably
many other antelopes from the parts of tropical
Africa which are rather semi-arid grass-land than
desert.

In desert of an extreme tjrpe many of the animals
have perforce to dispense entirely with drinking
water, and it appears that a certain number of
species never drink at all, and derive their whole
water-supply from the desert herbage, and possibly
the dew. In this category of total abstainers Abel
Chapman mentions the Addax (Fig. 35) and Oryx
(Fig. 36) antelopes and the Addra and Sudan
gazelles, all of them inhabitants of the Anglo-
Egyptian Sudan. He also states that on certain
small islands in the Red Sea Gazella arahica exists
as a dwarf race, not exceeding one-third of the
weight of the normal race, and that these islands
are entirely without water.

It is probable that this abiUty to dispense with
water is a character of many of the gazelles (Fig. 37),
and that it accounts for the fact that species of the
genus are found almost throughout the Great
Palsearctic Desert.

Grinnell and Dixon state that the Round-tailed
Ground Squirrel {Citellus tereticaudus) does not drink
even when it has the opportunity ; another species,
the Desert Antelope Ground Squirrel (Ammospermo-

ANIMAL LIFE IN DESERTS

philus leucurus), can last for several months between
drinks, but does drink, in nature, when water is
available. We know almost nothing of the water
needs of our Old World rodents. I have already
recounted observations made on a captive Egyptian

Fig. 35. — Addax Antelope (Addax nasomaculatus), Male, from the

Sudan.

{Drawn from life by Miss A. M. Gayton.)

Jerboa in London : Cheeseman kept captive speci-
mens of a different species (Jaculus loftusi) in Basra,
Mesopotamia, in summer, and remarked that " they
drank frequently, taking small sips in their f orepaws.
This is remarkable, as their earths are often placed

Fig. 36. — Arabian Oryx {Oryx leucoryx), an Inhabitant of Waterless

Sandy Desert.

{Drawn from life by Miss A. M. Gayton.)

Fig. 37. — Persian Gazelle {GazelJa subgutturosa), from Kirkuk, Perso-

Mesopotamian Frontier.

(Dream from life by Miss A. M. Gayton.)

92 ANIMAL LIFE IN DESERTS

where both dew and water would be to all appear-
ances unobtainable." Probably, therefore, this Jer-
boa is to be grouped with the animals which do
drink, but need not do so. The Gerbil Meriones
swinhoeii, from the flat stony uplands of the Afghan
Border, refuses water in captivity (C. M. Ingoldby).

According to Camp, most American desert reptiles
require no water, and this must be true of many
which occur in the Great Palaearctic Desert : my
correspondent, Capt. G. W. G. Kingston, suppUes a
good example in the Agama, which frequents the
ruins of Ur of the Chaldees in Southern Mesopotamia,
a dusty spot far from the River Euphrates or any
well, and without rain or vegetation for at least
seven months in the year. The lizard Moloch
horridus of West and South Australia, a repulsive
animal covered with tubercles and spines, has the
power of absorbing water through the skin after a
fall of rain. The Gecko (Eublepharis macularis),
which occurs in Persia and North-west India,
drinks freely from a saucer in captivity (C. M.
Ingoldby).

As our knowledge of the biology of the smaller
forms of desert Ufe increases we shall no doubt find
remarkable instances of abiUty to exist without
moisture. The case of a Stratiomyid fly {Hermetia
chrysophila), the larvae of which are able to endure
at least fifteen months without food or water, and
which eat decayed cactus joints whenever moisture
is present, is probably typical of a large number of
other insects.

ANIMALS— PHYSICAL ENVIRONMENT 93

ii. Fauna op Waters in Deserts

Conditions of life in a permanent well or spring
in the desert, or in a river which runs for part of its
course through desert, are not in any way different
from those which prevail in similar situations
elsewhere, and the animals of these springs and rivers
do not concern us. But there are other and more
temporary water-places in deserts, and those of
them which are liable to be filled with water at
fairly regular intervals support a very interesting
fauna.

The inhabitants of the temporary pools are exposed
either to death or else to the full rigour of the desert
climate for many months on end, while the pools
are dry ; and even when they are j&Ued with water
the position of the animals is precarious, because the
period which they will be able to devote to active
life, to feeding and to reproduction, is a short one.
Moreover, during the gradual drying up of their
pool the saltness of the water increases : so that the
animals are faced with three separate problems — the
ordinary problems of Hf e in fresh water, the gradually
increasing salinity of their water, and its eventual
disappearance.

Certain groups of animals, abundant in the fresh
water of other climates, are entirely unable to solve
these problems. The Newts, for instance, are found
all over Northern Europe and Asia, but they are
limited in a southward direction by the northern
edge of the Great Palsearctic Desert, and no newt
appears to have penetrated or crossed it. It would

94 ANIMAL LIFE IN DESERTS

be interesting to study the effect of belts of desert
upon the distribution of leeches, planarians, and
other naked damp-skinned animals.

Other animals are unable to survive the desicca-
tion, but become temporary colonists of water-holes
in deserts and when the water dries up are locally
exterminated. Among them are denizens of per-
manent waters, which are occasionally introduced
into a temporary pool by floods ; this is an accident
of common occurrence to small fish, and doubtless
to a large number of other forms of life. Winged
insects also, whose early stages are passed in waters,
frequently colonize these temporary pools. This
temporary colonization is of course most commonly
seen in parts of the desert close to permanent pools
or rivers : temporary pools in such places are
invaded by many forms of gnats and mosquitoes,
by gad-flies (Tabanidse) and by dragon-flies. It is
probable that the Tabanidae and dragon-flies seldom
pass successfully through their early stages, which
are of long duration ; but the gnats and mosquitoes
frequently pass rapidly through several generations.
As the pool shrinks in size and increases in saltness
it becomes a fit home for the larvae of small fhes of
the family Ephydridae, and these are sometimes
present in enormous numbers.

But it is the permanent inhabitants of these
temporary pools which are most interesting, because
their methods of solving the problems which confront
them are so varied. The Phyllopod Crustacea
(e.g. Apus and Estheria) exist through the drought
as eggs, and can survive a period of drying which

ANIMALS— PHYSICAL ENVIRONMENT 95

extends over years. Recurring periods of drought
are necessary for their existence, so that it is not
remarkable that they should be found in deserts
and semi-deserts in nearly every part of the globe.
One member of this group, the Brine Shrimp
(Artemia), is not only extremely resistant to drought
in the egg stage, but also requires for its development
water nearly or quite saturated with salt ; and it is
found in temporary salt pools in many parts of the
world, both in deserts and other situations. Certain
Phyllopods are capable of extremely rapid growth
when the mud in which their eggs have been dormant
is flooded, and when the shallow pool is heated by a
desert sun. Spencer records that Apus in Central
Australia reaches a length of 2^ inches in fourteen
days after rain falls.

Other inhabitants of temporary pools descend into
the mud when the pool dries up, and there continue
to exist. Examples are the crab (Telphusa) and
crayfish (Astacopsis) of Central AustraHa, and many
water-beetles and molluscs. Of the Gasteropod
molluscs many are protected by an operculum, with
which to close the mouth of the shell : Isidorella
newcombi, in water-holes in Central Australia, plugs
the shell with mud, which is probably specially
prepared by passage through the ahmentary canal.

The biology of the frogs found by the Horn
Expedition to Central Australia has been treated
at some length by Spencer. Among the species
collected were some which showed marked abiUty
to breed rapidly and take advantage of a short
favourable period, and others whose habits enabled

96 ANIMAL LIFE IN DESERTS

them to survive drought in a remarkable manner.

That frogs are able to exist at all in temporary
waters in Central Australia is very remarkable,
because their need for water is great, and their
damp skins are entirely unsuited to Ufe in a dry
atmosphere, in which they invariably die. Six
species were found in the desert region, but two
were rare and little was discovered about their
habits. The remaining four all showed different
interesting methods of overcoming the hostiUty of
their environment. They were all of them able to
spawn at any time of year, as soon as rain had fallen.

Hyla rubella^ a close relative of the green Treefrog
of Southern Europe, was found in nearly every
water-hole which was visited during the dry season.
It appears that it does not burrow in damp soil,
and therefore when its water-hole dries up it perishes.
On the other hand, it is a very rapid breeder, and if
rain falls heavily its tadpoles are carried down the
channels and its range is, for the moment, very
greatly increased. It is therefore a species which
depends for its success in colonizing Central AustraUa
on its abiHty to produce its young rapidly and in
large numbers : it might be said to be successful
because its high birth-rate after rain exceeds its
high death-rate diu-ing the dry weather. If the
drought exterminates a colony of this frog at a
certain water-hole in the bed of a stream, the next
flood will enable the species to colonize the same
spot once again from a permanent pool.

Another common frog was Limnodynastes ornatus.
Like many of the frogs of the more arid parts of

ANIMALS— PHYSICAL ENVIRONMENT 97

Australia this species is able to excavate burrows in
soft soil. These it makes in sandy places in the
beds of temporary streams, and it reaches a layer of
damp sand even though the stream has been dry
for a long time. The burrows are not permanent ;
a fresh one is made for each day, and at night, when
the temperature is low and the humidity high, the
animal ascends to the surface to hunt for beetles.

Heleioporus pictus is another burrowing form, but
it makes permanent burrows. In these it exists
for months at a stretch during periods of drought,
I am informed that the eggs are laid in the burrow,
about 18 inches deep in the sand, in a foamy mass.
Development occurs in the egg to such a stage that
the tadpole is ready to emerge as soon as rain faUs.
The albumen of the egg is hygroscopic, and when
moisture is abundant it is absorbed in such quantities
as to burst the membrane which covers the egg, and
release the tadpole.

Chiroleptes platycephalus resembles the last species
in making a permanent burrow and in its abiHty to
exist in it through a long period of drought. It
possesses also remarkable powers of storing water,
and it can contain a very considerable quantity in
its urinary bladder, subcutaneous tissues, and peri-
toneal cavity ; when it is fully charged with water
it is almost spherical. It makes permanent burrows
to the depth of about a foot in soil which will shortly
be baked by the sun into a mass of hard clay, and
here it remains for the dry season. By means of
its burrowing and its powers of storing fluid it is
able to resist long droughts ; permanent springs and

98 ANIMAL LIFE IN DESERTS

pools are unsuited to it, and it is only found in places
in which it will be exposed to desiccation periodically.
This animal can contain so much fluid that it is
occasionally used by the Australian aborigine as a
source of drinking-water. It appears to imbibe the J
water through its skin, as weU as its mouth, and to
do so very rapidly ; an AustraUan friend, Mr. L.
Harrison, writes to me that if you " put a lean, dry,
herring-gutted Chiroleptes into a beaker with 2 inches
of water, in two minutes your frog resembles a
somewhat knobly tennis-ball."

iii. Heat and Relative Humidity

These two factors must be considered together
because under natural conditions a high temperature
and a low relative humidity are generally associated
(page 23). It is not therefore possible, in the
absence of experimental work, to discriminate
between the effects of the two.

The very existence of small animals on the surface
of the desert at midday is remarkable. Most of
these animals — for example, the Hzards and beetles
— are cold-blooded, so that one supposes that their
temperatures approximate to that of the air in
which they find themselves at any given time ;
and as they are relatively small the fluctuations of
their internal temperatures must be rapid. In
spite of this, animals do manage to exist on the
desert soil even in the middle of the day in summer.

Good examples among the reptiles are the Agama
lizard at Ur of the Chaldees, to which reference has
been made (page 92), and the Chuckwalla (Sauro-

ANIMALS— PHYSICAL ENVIRONMENT 99

malus), a vegetarian lizard of the Calif ornian deserts
which sits upon rocks when they are too hot for
the hand to touch (Camp).

Many insects have the same power of Hving on
the surface of the soil at midday, even during the
hottest season. On June 2, 1922, I observed at
Jericho, Palestine, at noon that the shade tem-
perature was 90° F. (32-3° C), and the surface of
the hard clay soil 124° F. (50-8° C), and on it two
species of mantis larvae (Eremiaphila and Fischeria),
and adults of a Short-horned Grasshopper, were
moving about. In deserts nearer the Equator
much greater surface temperatures (page 21) are
attained, but these figures serve to show the degree
of heat to which the insects, etc., are exposed on
the bare desert.

The case of the diurnal mammaha of the desert
is very different, and their survival of summer
midday conditions is not so remarkable. Such
animals as hares, gazelles, and camels are large, so
that in any case they would not be exposed to
very rapid fluctuations of internal temperature :
they are, moreover, warm-blooded, that is to say,
provided with a mechanism which maintains their
bodies at or near a constant temperature : there-
fore fluctuation of air temperature affects a gazelle
or camel, or even a hare, very much less than it
affects a Hzard or beetle; so that the power of
j the mammals to survive the midday heat is less
i remarkable than their ability to provide themselves
I with water, by the evaporation of some of which
! they maintain their "normal temperature."

100 ANIMAL LIFE IN DESERTS

On the other hand, to many desert-dwellers ex-
posure to the climate at midday is very rapidly
fatal. The Horn Expedition to Central Australia
observed that if the hzard Tiliqua was taken from
its hole and put on the sand at noon it ran a few
yards and rolled over dead, and similar examples
might be multipHed. The animals which are unable
to survive surface conditions at midday resort to
various devices in order to reach a more equable
temperature and humidity than is prevalent in the
open air. A few birds obtain all the shelter they
require by getting into the centre of trees and bushes.
Thus in the plain of Jericho the Great Grey Shrike
{Lanius excuhitor aucheri) and the black and white
Wheatear {Saxicola lugens) take refuge during the
heat of the day in midsummer in the bottoms of
bushes of Atriplex and Zizyphus (Fig. 25). At all
other times they are most conspicuous birds, the
Shrike perched on the top of a Zizyphus, and the
Wheatear in any unprotected position. In a similar
way one may observe House Sparrows {Passer
domesticus hiblicus) and White-cheeked Bulbuls {Pyc-
nonotus leucotis mesopotamice) bury themselves during
summer days at Basra in the dense mass of leaf-
bases and young shoots which spring from the
crown of a date-palm.

Many small animals take refuge under stones and
in similar places, particularly at the seasons when
traces of moisture are still present. In the Great
Palaearctic Desert, wherever mixed stones and earth
occur (page 47), a large collection of small animals
may be obtained by turning over stones during the

ANIMALS— PHYSICAL ENVIRONMENT 101

spring and early summer. One obtains such crea-
tures as woodlice ; millipedes and centipedes ;
spiders, scorpions, mites and pseudo-scorpions ;
lepismids, Japyx, earwigs, cockroaches, crickets,
very numerous beetles, bugs, ants ; snails and
occasionally slugs, and earthworms. What befalls
these animals in the hot and dry season is largely
a matter of conjecture. Probably some descend
deep into cracks in the soil, and others aestivate
in the egg and possibly in other stages. Spencer
attributed the existence of land-snails in Central
AustraUa to various factors in different species.
Some existed on the shady side of hills, others
sestivated among tree roots, others closed the mouth
of the shell with a plug of mud ; others again were
minute and descended deeply into the clefts in
the soil. It is at any rate certain that the rich
fauna that one finds under stones in Persia, Pales-
tine, Algeria, and other stony deserts, in spring-
time is almost as ephemeral as the annual flowers,
and it is very remarkable that such moisture-
loving forms as snails and earthworms should be
able to exist through the summer in any stage in
these countries.

The geographical distribution within the Great
Palaearctic Desert of these multitudes of smaU
creatures depends among other factors on the
presence of stones under which to shelter, and of
regularly recurring rainfall, but a very similar associa-
tion may be found in Lower Mesopotamia, a stoneless
plain consisting of nothing but the finest silt carried
down by the Tigris and Euphrates ; in this country

102 ANIMAL LIFE IN DESERTS

a fauna is found after rain, between the trunk and
the leaf -bases of the date palm ; this fauna is rela-
tively rich and contains all the groups which I have
just enumerated as characteristic of stone and earth
desert in spring. In fact, one may say that the
animals which shelter in the date-palm in Mesopo-
tamia are the biological counterpart of those found
under stones in Persia or Palestine. To what
extent the same genera or species of animals are
represented in both we do not at present know.

Other animals which are unable to endure the
climate of the surface of the desert dig burrows
or use burrows which have been excavated by other
creatures. They thus easily reach a zone in which
temperature and humidity are nearly constant
(page 22). In the group of active burrowers fall
certain lizards and snakes, and nearly all the small
rodents (Jerboas, Gerbils, Spiny Mice, and many
others), and some at least of the small marsupials
of Central AustraHa. Many observers have not" ed
the extraordinary abiUty of the House Mouse (Mus
musculus) and its very close relatives {Mus gentilis
and other forms) to colonize human habitations
in nearly every part of the Great Palaearctic Desert :
the rapidity with which they become abundant in
isolated camps in Mesopotamia was frequently
noticed. These animals are protected from great
fluctuations of heat and relative humidity by their
burrows which are made beneath houses, and be-
cause they frequently travel from place to place
in boxes and bales. If they were diurnal and Uved
openly in man's habitations they would be faced

^ >»

ANIMALS— PHYSICAL ENVIRONMENT 103

with such fluctuation of temperature and humidity
as might prevent their colonizing houses in the
desert.

Many of the small wild rodents close the mouths
of their burrows by day with a plug of earth, and
no doubt this tends still further to stabiHze the
cUmatic conditions which prevail in the burrow.
Detailed observations on this point are lacking for
many species, but among rodents which plug the
burrow one may mention Dipodillus dasyurus and
Jaculus loftusi and Nesohia huxtoni in Mesopotamia,
and the American genus Dipodops ; among those
which leave the burrow open are Jaculus (species ?)
in Palestine, and Dipodomys deserti (Fig. 38) in the
American deserts. That the conditions in a burrow
are widely different from those which prevail out-
side is sufficiently shown by Pitman's observation
on the Jerboa, Jaculus loftusi, in Lower Mesopotamia.
This species is absolutely nocturnal. " Their earths
go steeply into the ground for 2 or 3 feet and the
Httle creatures evidently lie up all day in the cool,
damp earth as I always noticed that captive speci-
mens, of which we tried to keep many from time
to time, suffered tremendously from the great heat
during the day, even when kept in the coolest of
places dug right into the ground, so much so that
we never managed to keep any alive for more than
a few days."

Among the burrowing insects one must mention
two groups, the Crickets and the Ants. Species
of Cricket (GryUidse) are often found even in the
more barren parts of the Great Palaearctic Desert ;

104 ANIMAL LIFE IN DESERTS

they take refuge by day in burrows dug under
stones, and issue forth at night when the air is cool
and the humidity not very low : the ants have
successfully overcome the cHmatic difficulties, and a
number of species may be found in the Great Palae-
arctic Desert and in Central AustraUa ; many of
them come up from their subterranean nests in
the morning and late evening, but others are active
during the heat of the day.

In the group of animals which uses burrows
constructed by other animals are included the
majority of desert snakes and Uzards (at any rate
in the Great Palaearctic Desert) and a number of
nocturnal beetles (especially some Carabidae and
such Tenebrionidse as Blaps).

Many larger creatures, whose powers of movement
enable them to rest at some distance from their
feeding-grounds, take refuge in caves. Conditions
in a cave differ fundamentally from those prevailing
in the open desert : in the cave, temperature is
nearly constant, humidity is more constant and
higher than in the desert, and Hght is absent (C. B.
WiUiams). But for the presence of caves the
existence of bats in desert areas would be impos-
sible, but in deserts in which caves occur, particu-
larly if drinking-water is available, bats are fre-
quently numerous, both as species and as individuals.
Birds which nest or which roost in caves are quite
an important element in the fauna of the Great
Palaearctic Desert : examples are sub-species of
the Eagle Owl {Bubo bubo) and Little Owl (Athene
noctua), and of the Swifts (Gypselus apus, 0. murinus,

ANIMALS— PHYSICAL ENVIRONMENT 105

and C. affinis), and of the Rock Dove {Columba
livia).

None of these sub-species are very highly modified
for hfe in the desert, and the species from which
they are derived are distinguished for their abiUty
to Hve in many types of cUmate and country ;
in fact, the two owls, the dove, and the Common
Swift all breed as far north as Northern Europe.
It seems that the presence of caves, with their
relatively unvarying temperature and humidity,
may have enabled these vigorous and adaptable
species to penetrate a short distance into the desert.
Certain of them now breed and roost in houses
and ruins, but this is clearly only a slight extension
of the cave-haunting habit.

It is probable that a closer study of the cave fauna
in such countries as Egypt and South Palestine
would reveal most interesting forms of Hfe. The
contrast in cKmate between open desert and cave
is so great that the colonization of the cave by
animals which are specialized to hve in the sur-
rounding desert would present great difficulties.

The eggs of birds which breed upon the surface
of the desert and are exposed to its summer climate
are in a position of great danger, because if they
are left uncovered by the parent birds they are
rapidly killed by the heat during the daytime.
It should be remembered that, at any rate in the
Great Palsearctic Desert, most of the birds breed
during the hot weather, e.g. Sandgrouse (page 85),
Common Pratincole, and others. It is only the
largest of eggs, those of the ostrich, which can

106 ANIMAL LIFE IN DESERTS

survive prolonged exposure to the desert sun.
Though it is extremely difficult to disentangle truth
from fiction in the case of the wild ostrich, I think
that the following facts are now established. Neither
in Africa nor in Arabia do ostriches bury their
eggs in the sand, as is frequently stated. The
eggs are often left entirely uncovered and exposed
to the heat in the middle of the day, particularly
in the hotter parts of the bird's range. At other
times of the day, and particularly in the colder parts
of the bird's range, the eggs of the ostrich are
incubated by both parents in turn.

Smaller eggs, which are more rapidly penetrated
by heat, are quickly killed under conditions which
merely serve to incubate the great eggs of the
ostrich. The existence of this danger was clearly
demonstrated during the fighting round Kut el
Amara, and in other places in Mesopotamia, where
many eggs of Sandgrouse were destroyed by the
sun because the parent birds were driven from
their eggs by gunfire.

C. B. Ticehurst tells me that such eggs as those
of Geochelidon nilotica, Glareola pratincola. Sterna
caspia, and Larus gelastes are killed by exposure to
hot sun. These birds are not desert breeders, but
nest upon mud-banks under conditions which fre-
quently approximate to true desert during the
breeding season, and his observations are therefore
pertinent.

The devices to which the parent birds resort
to avoid such fatalities are extremely interesting
because they are so varied. Many desert breeders

ANIMALS— PHYSICAL ENVIRONMENT 107

place their nest as far as possible under shelter,
most Larks under a small bush, all Wheatears in a
hole or small cave, Hey's Partridge and See-See
(Ammoperdix) in holes in small cliffs, or under
boulders. Of the birds which breed in the open
without protection from rocks or bushes, most
species sit upon the nest from the time the first
egg is laid. The eggs are therefore kept at a nearly
constant temperature by the bird's body, and are
not exposed to the heat by day and the cold by
night. It appears to be established that Sand-
grouse incubate from the time of laying the first
egg, though Meade-Waldo's observations in an
aviary in England do not support this view.

It is recorded that the Pratincole (Glareola pra-
tincola) stands over its first egg, and by doing so
protects it from the sun's rays, and that a small
Tern (Sterna saundersi) which breeds on the bare
shore at Karachi (Sind) does the same.

After incubation has commenced the majority
of desert birds are unwilling to leave their eggs,
and if they are compelled to do so they return
to them as quickly as possible. This has been
noticed by several observers of the Coiu-ser (Cur-
sorius gallicus) and Sandgrouse. The eggs of the
Sandgrouse have additional protection from heat,
for when one parent returns from watering, and
reheves the other from the duty of incubation, its
breast is saturated with water. Therefore it appears
that the eggs and the soil on which they are laid
are wetted every day, which must tend to prevent
overheating.

108 ANIMAL LIFE IN DESERTS

The Kitlitz Plover (Charadrius pecitarius), which
breeds in tropical Africa and which extends down
the Nile Valley to Lower Egypt, and its relative
Charadrius alexandrinus seehohmi cover their eggs
with sand when they leave them. The purpose of
this is unknown : it may be protection from foes
or from the sun's heat.

iv. Animals and Wind

We have already seen (pages 27-30) that wind
is a constant element of the desert cUmate, at any
rate in summer. It is frequently strong, and even
violent ; in many places it is constant in direction,
and under certain circumstances columnar vortices
are formed which sweep small objects from the
surface of the desert and carry them to a great
height. It is probable therefore that wind is a
great distributor of the seeds of desert plants, and
of all the smaller forms of animal life. The great
majority of the creatures which it carries before it
or sweeps up into the sky are doubtless killed by its
violence, but of those which survive a smaU number
reach a suitable environment far from their original
home.

It seems probable therefore that wind has had
a large share in widening the distribution of many
of the plants and animals of the Great Palsearctic
Desert, and it is important to remember that the
desert wind is barely if at all impeded by herbage
and grass, as it is in other types of country. It is
therefore felt in its full force even by the small
forms of life on the surface of the ground.

ANIMALS— PHYSICAL ENVIRONMENT 109

The effect of the wind upon the flora Indirectly
affects the fauna. To the plants it is harmful
both by reason of the physical damage done by
violent gusts and wind-blown sand and small
pebbles, and also because it rapidly dissipates the
sHghtly moist air which accumulates round the
plant owing to transpiration. Increased transpira-
tion results, that is to say, increased loss of water
which is already very scarce : it foUows that plants
may be able to exist on a specified amount of water
if they are protected from wind, and may be killed
if they are exposed to the wind.

This is well seen wherever a wind of constant
direction blows through a narrow valley ; any
large rock which breaks the force of the wind,
and thereby reduces evaporation and transpiration
under its lee, shelters a richer flora than wiU be
found elsewhere.

It is in fact true that places exist which are desert
primarily because of wind. For instance, through-
out great parts of the Libyan Desert the distribu-
tion of plants is determined rather by the presence
of shelter from wind than by any other influence.

The effect of a strong wind loaded with sand upon
the very scanty spring vegetation on the Libyan
border of Lower Egypt is thus described by Thomas.
"On April 13, towards the close of the growing
period of most plants, a hot wind blew in from the
desert for about five hours, raising great clouds of
sand which drove along the surface of the groimd
like mist. The temperature went up considerably,
in spite of the sun being obscured, and was over

110 ANIMAL LIFE IN DESERTS

45° C. : the air felt intensely dry and was charged
with sand-grains which produced a smarting effect
on the exposed skin. The wind went down during
the night, but it remained hot and no dew fell.
The storm continued in this way for the next two
days, and its effect on the vegetation was very
striking. All flowers and young parts of plants
had shrivelled, the upper portions of the green
branches of Calligonium had died and had often
been broken off, the fruits of this plant had dried
and had become quite hard : most of them were
detached from the plants and were blown about
in all directions. The upper portions of the stems
of Heliotropium luteum were withered and dead,
and had lost all the younger leaves. AU the plants
appeared very much withered, except Imperata
cylindrica, which seemed untouched. Many plants
seemed partially uprooted, especially PuUcaria and
Polygonum ; in reahty the wind had removed the
surface layers of the sand round them, and 20-25 cm.
of rootstock were exposed — this showed the im-
portance of being deep-rooted. The surface roots
of Panicum turgidum were very frequently laid bare.
In other cases plants were wholly or partially bm^ied."
The direct effect of wind upon the animals,
especially the smaller animals, also merits discussion,
as it has apparently caused modification of habit in
some animals and of structure in others. Certain
small Blue Butterflies (Lycaenidae) which inhabit
the Great Palsearctic Desert possess the power of
continued flight within one small bush, from the
shelter of which they seldom issue. Butterflies of

ANIMALS— PHYSICAL ENVIRONMENT 111

the genus Tarucus may be observed flitting up and
down continuously inside a bush of Zizyphus, with-
out leaving the middle of the bush, and sometimes
continuing in flight for many minutes. The minute
Chilades galba, another member of the same family,
is able to limit its flight within a plant of Ononis
(" Rest Harrow "), which is only a foot in circum-
ference, and to remain on the wing in this Uttle bush,
when such a wind is raging outside as to prevent
the flight of all other butterflies.

Another interesting modification of habit has been
observed by Hartert, Rothschild, and others in the
Algerian Sahara. The prevalent wind is from the
east, so that the sand and debris which it carries
settle on the west side of any bush or stone, because re-
lative calm prevails under the lea of the bush. Several
species of Passerine birds regularly make their nest
against the windward side of small bushes, and so
avoid being smothered with sand and debris. They
then fortify the outer side of the nest with a mass of
pebbles, apparently in order to protect the nest
from wind. This seems to be the invariable habit
of Clot-bey's Lark {Rhamphocorys clot-bey), which
collects pebbles weighing as much as half an ounce.
In the Larks Ammomanes phoenicurus arenicohr and
Eremophila alpestris hilopha, the habit of placing
the nest on the windward side of a smaU bush is
apparently universal, but the barricade of stones is
occasionally very small or quite absent. The nests
of the Trumpeter Bullfinch {Erythrospiza githaginea
zedlitzi) are invariably on the windward side of small
bushes, and perhaps protected by their position

112 ANIMAL LIFE IN DESERTS

immediately under the bush, for they were without
a barricade of stones. One species of Wheatear
(Saxicola leucura) has a similar habit, nesting under a
rock and almost blocking the passage to the nest
with a mound of pebbles : the bird does this in the
Algerian Sahara, and also in the Sudan. Another
Wheatear {8, leucopyga cegra) shows what is probably
a development of the same habit, for it nests in holes
in rocks and crevices in walls and constructs a wide
path of flat stones up to the mouth of the crevice.

Similar habits have been observed in other
countries, but no information is given as to the
direction of the prevalent wind, or the side of the
bush under which nests were habitually built. In
the Sudan Chapman has recorded the building of
barricades by an Ant-Chat (Oercomela scotocerca)
and a Lark {Ammomanes deserti), and states that
the Cercomela collects as many as 130 pebbles in
its barricade. This habit is the more remarkable
as it has been developed by birds which are not
closely related to one another ; one presumes that
it has originated independently in the Finch, in the
Wheatears and Ant-Chat which are closely related,
and at least once among the Larks.

Of modifications of structure which are apparently
induced by the wind, the most striking is the
winglessness of many insects whose near relatives
in other types of country are winged. In the order
Orthoptera one may observe several series of insects
in which the wings are progressively reduced. Some
species have the wings so shortened that they are
useless for flight, but normal in structure and

ANIMALS— PHYSICAL ENVIRONMENT 113

proportions ; in others they are present as minute
vestiges, or so reduced that their sole function is to
assist in the production of the insect's chirrup.
In some species the reduction has proceeded much
further in one sex than in the other. Short-winged
forms may be observed in the Long-horned and
Short-horned Grasshoppers, in the Mantis family,
and in the Crickets, so that they must have arisen
independently many times in the Orthoptera. The
phenomenon is not by any means confined to desert
species, but is much more frequently seen in them
than in those of other environments. For instance,
in Algeria and Tunisia about half the Orthoptera
are wingless, even when the forms which inhabit the
fertile coastal region are included in the count.

Among the Coleoptera (Beetles) fusion of the
wing-cases and consequent flightlessness is a char-
acter of very many Tenebrionidse (Fig. 42, facing p.
150) and Carabidae (Ground Beetles) in deserts. Loss
of the power of flight in these two families of beetles
and in the Orthoptera is not confined to species
which inhabit deserts, but is much more common
among them than among others. That it is due
solely to the wind and not to any other infiuence is
apparent from the fact that a similar loss of the power
of flight occurs in many other environments which
are exposed to violent winds, but do not in any
other respect resemble deserts : the insects of
mountain tops and of small isolated islands furnish
examples.

The dispersive effect of the wind upon small
animals can be exercised in the absence of any modi-

114 ANIMAL LIFE IN DESERTS

fications either of structure or of habit. This is seen
in the case of caterpillars of the famiUes Arctiidae,
Lymantriidae (Liparidae), and Lasiocampidae. These
hairy caterpillars are abundant in the semi-deserts
of Algeria, Southern Palestine, and other countries
in the spring-time. In places where the annual
vegetation is not too dense one may see them roUed
up and blown along the ground for many yards by
a gust of wind. They are not more hairy than their
congeners in Europe, so that in this case we have a
number of insects which are able to benefit by the
desert winds without modifying either their habits
or their structure.

Of the destructive effect of desert wind upon small
creatures, especially small winged creatures, very
little is known. It is on record that small birds
have been dashed against a waU and killed in the
Hebrides, and there is every reason to suppose
that the violent winds which occasionally visit some
deserts are equally destructive. The destruction of
swarms of locusts by wind which blows them into
the sea has been famihar since the dawn of history.

V. Relationships with Soil

There is no doubt that each type of desert soil
presents its special problems to the fauna and flora
and is inhabited partly by generaHzed forms which
are able to exist in many types of desert or even
outside the desert, and partly by specialists which
are limited to clay or rock or sand, or other special
soil. Information on these points is at present very
meagre and fragmentary, except with regard to the

ANIMALS— PHYSICAL ENVIRONMENT 115

fauna of sandy desert. To that, therefore, I propose
to confine our attention entirely.

It has been shown (page 40) that sand probably
presents more difficulties to the desert flora and
fauna which attempt to colonize it than does any
other type of desert. It is not, therefore, to be
wondered at that the fauna of sandy areas, and
particularly of areas in which the sand is loose, is a
small one, and that it consists largely of animals
which in overcoming the difficulties of life in sand
have become unfitted for life in any other environ-
ment.

Grinnell has described the conditions of life
of certain species of sand-living rodents in the
North American deserts. The Round-tailed Ground
Squirrel (Citellus t, tereticaudus) requires large areas
of sand, and also bushes, under which it can burrow :
it is frequently abroad in the daytime, but it avoids
direct sunshine by passing rapidly from the shade
of one bush to that of another. It cannot endure
the fierce heat of midday on bare sand, and if an
individual is caught in a trap uninjured but exposed
to the sun's rays it dies quickly. This rodent is
therefore an animal which requires the co-existence
of a geological and floristic factor, in order to enable
it to live in a particular place. The Big Desert
Kangaroo Rat {Dipodomys deserti, Fig. 38) lives in
the same sandy places as the Round-tailed Ground
Squirrel, but its requirements are quite different.
It is nocturnal, and is sheltered in its burrow from
the conditions which prevail during the day; it
is therefore indifferent to the presence of bushes.

116 ANIMAL LIFE IN DESERTS

What it requires is blown sand which must be at
least a foot deep. The probable explanation is that
sand is the only soil in which it is able to burrow ;
for its incisors are weak, and its claws and feet smaU.
In fact, what determines the presence of this rodent
in a given spot is the coexistence of two physical
factors, loose sand for its burrows, and sufficient
depth of sand to accommodate it.

Associated with the Big Desert Kangaroo Rat,
and largely dependent on it for food, one finds the
Kit Fox ( Vulpes macrotus arsipus), which is a purely
desert animal and apparently occupies the same
place in nature in the American sandy deserts as the
Fennec Fox in Africa. The Fennec Fox {Vulpes
zerda) Uves exclusively in sandy places in the Sahara
and Egypt ; it is a small, rather weak fox, which
feeds upon beetles, grasshoppers, vegetable matter,
and a few small rodents.

The Marsupial Mole (Notoryctes) of Central Aus-
traUa is an inhabitant of sandy places. It possesses
the general outward form of our own Mole (Talpa),
and of other burrowing mammals, to none of which
is it in any way related. It is a cyUndrical animal,
with strong shovel-shaped feet, and a reduced tail,
and it has no eyes. It makes no definite runs,
because the sand collapses at once after its passage,
but it spends its time pushing through the sand in
search of insects, particularly ants. The Tuco-tuco
(Ctenomys), a rodent of South America, exhibits
many of the external characters of the mole, though
it is related neither to the mole nor to Notoryctes.
It is found in isolated colonies wherever sandy

ANIMALS— PHYSICAL ENVIRONMENT 117

patches occur in the pampas and semi-deserts of
South America, and there is a tendency for the
individuals of each colony to differ in colour, size,
and other characters from those of other colonies.

The reptiles found in sand are pecuUarly interesting
because they show many examples of convergence.
Camp, in describing the habits of the reptiles of
South-Eastern California, states that in one burrowing
snake and three lizards the rostrum is specially
developed, protruding beyond the mouth. These
lizards belong to several different families, so that
this similarity in the rostrum is due to convergence
and not to close relationship.

The same enlargement of the rostrum has been
recorded by other authors in several different genera
of snakes which burrow in the light soil or sand of
arid regions : rather similar are the fringed scales
surrounding the eye in some sand-dwelling Uzards.
In the Jerboa (Jaculus) the muzzle can be contracted
and the nostrils narrowed and almost covered by a
fold of skin. It appears that the function of this
is to protect the nostrils when the animal is burrow-
ing and pushing soil with its broad snout (Anderson
and De Winton, and Pocock).

Certain lizards and snakes possess the power of
burrowing into sand with extraordinary rapidity.
The lizards which do so do not use their legs, but
progress by rapidly bending the body from side to
side. In members of the Skink family (Scincidse) in
North African deserts this is associated with pro-
gressive reduction of the Hmbs, and members of this
family exist showing various stages from the normal

118 ANIMAL LIFE IN DESERTS

complement of four legs to complete absence of
Mmbs.

Many lizards living in sandy places are extremely
rapid in their movements. When they are not
running they stand alert with the head held high
and the front part of the body raised on the fore-legs,
and when they are in motion the tail is held weU
above the ground as a counter-balance. This holds
good of lizards of several families, from several parts
of the world ; and the species which are predaceous
and those which are preyed upon both exhibit it.
In many of them the toes of the fore- and hind-feet
are broadened by a fringe of elongate scales. Appar-
ently aU of these species Hve on sand, some of them
on great stretches of dune, others on the small heaps
of blown sand which accumulate under bushes in
deserts of mixed stone and earth : it seems legitimate
to conclude that the fringe widens the surface, which
presses on loose sand and acts in the same way that
a snow-shoe does on loose snow. As Figs. 39 and 40
show, these fringes are developed in several families
of lizards, in deserts in different parts of the world.
Of the seven genera figured Phrynocephalus (A) is
an Agamid from Transcaspia ; Acanthodactylus (B)
and Scaptira (C) are Lacertidse, distributed in the
Great Palsearctic Desert ; CaUisaurus (D) is an
American Iguanid ; Teratoscincus (E), Stenodactylus
(F), and Ceramodactylus (G) are Palsearctic desert-
Hving Geckonidse. It is clear that this curious
character has been developed on at least half a
dozen different occasions, and it is clear also that it
is a response to Ufe on sand. I am most grateful

ANIMALS— PHYSICAL ENVIRONMENT 119

to Miss J. Procter, of the British Museum (Natural
History), for her kindness in selecting these most
interesting Hzards.
Among the insects, the ants which hve in sandy

'm=^

Fig. 39. — Fore -FEET op the following Lizards : — A. Phrynocephalus
mystaceus ( x 1^^). B. Acanthodactylus scutellatus ( X 2). C. Scap-
tira grammica (x 2). D. CalUsaurus (Uma) scoparius. After Cope,
" Amer. Nat.," 1894. E. Teratoscincus scincus ( X 2). F. Stenodactylus
guttatus ( X 3). G. Ceramodactylus dorice ( x 3).

and dusty places are remarkable. In very many
of them a " circum-oral crate " of stiff bristles is
developed upon the structures which surround the
mouth. The purpose of this is clearly not connected

120

ANIMAL LIFE IN DESERTS

with feeding, for it is well developed in harvesting
species, in predators, and in honey-pot ants (page 72).

Fig. 40. — ^Hind-feet of the following Lizards : — A. Phrynocephalus
mystaceus ( x 1^). B. Acanthodactylus scutellatus ( X 2). C. Scap-
lira grammica (x 2). D. CaUisaurus (Uma) scoparius. After Cope,
" Amer. Nat.," 1894. E. Teratoscincus scincua ( X 2). F. Stenodactylus
guttatus { x 3). G. Ceramodactylus dorice ( x 3).

Wheeler suggests that it is used to clean the strigil
on the fore-leg, which in turn is used for cleaning

ANIMALS— PHYSICAL ENVIRONMENT 121

the antennae, etc., and that it is only developed in
ants from sandy and dusty places because the
strigil is peculiarly likely to become clogged in such
places.

The protozoa of the sand in the neighbourhood
of Cairo have been investigated by Thomson and
Thomson. These microscopic animals exist in the
dry sand in a resistant envelope or " cyst," from
which they only emerge when the sand is moist,
and as it dries they again envelop themselves in
" cysts." In the climate of Cairo their period of
activity is reduced to a few days a year, and their
period of dormancy is extremely protracted. They
are exposed to light and heat and drought in the
sand, and yet the investigators were able to recover
about fifty species from the sand after eight months
of drought. Most of them belonged to forms known
elsewhere from fresh water ; that they were depend-
ent on occasional moistening is shown by their great
rarity in the sand of Luxor in Upper Egypt, in an
area which is without rain in the average year.

CHAPTER VI

RELATIONS BETWEEN ANIMALS AND
PLANTS

Interrelationships between animals and plants
may be divided into that class in which the animal
is dependent on the plant, and that in which the
plant depends upon the animal. The first group
of relationships is the larger, in deserts as in other
types of environment. AU the world over it is
true that the animal depends on the plant for
compounds of nitrogen and compounds of carbon :
most of the essential food of every Uving animal
comes directly or indirectly from plants, and with
it the animal swallows a proportion of water. The
plants also fulfil certain subsidiary functions with
regard to the animals; they furnish them with
shelter from the elements, and protection from
enemies. One may therefore say in general terms
that the plant provides the animal with food and
water, and with shelter and protection.

It is convenient to consider at one time the food
and the water which animals in deserts derive
from the plants which they eat. The food and
water are swallowed together, and may for the
moment be regarded as a single contribution made

122

1.^

RELATIONS OP ANIMALS AND PLANTS 123

by the plant kingdom to the animals. It must be
remembered that in the desert this source of water
is of much greater importance than it is imder
other conditions. In most environments the water
which is part of the food material is incidental :
in the desert it is essential, and commonly the only
available supply.

We have already (Chapter III) divided the
desert flora into three biological groups — the annuals,
the perennials which he buried during the un-
favourable season, and the perennials which exist
above the surface of the ground at all seasons.
Let us see how each of these groups is used by the
animals as a source of food and water.

The conditions which are best for the annuals,
and which lead to the production of abundant annual
vegetation after rain has fallen, are favourable also
to many animals. No sooner have the young annual
lants appeared above the earth than they are
attacked by numbers of caterpillars, bugs, leaf -eating
beetles, wood-Hce, and other plant-eaters : as soon as
the blossoms open they are visited by bees, butterflies,
moths, thrips, flower-eating beetles, and many other
small creatures in search of nectar or pollen or
petals. For a very short time the cUmate and the
floral environment is favourable to insects in
general. Then the soil dries, the air becomes hot,
and most of the flowers and insects disappear.

The majority of insects which are dependent on
the annual vegetation in the Great Palaearctic
Desert are active for a very short period and exist
through the dry nine months of the year in a state

124 ANIMAL LIFE IN DESERTS

of dormancy, some of them as pupse, others as eggs,
others probably as resting larvae. A few species
prolong their season of activity and produce a
series of broods by utiUzing first one food plant and
then another, as the plants successively become
available. A good example is furnished by Papilio
machaon, the Swallow Tail Butterfly, in Mesopo-
tamia. In April and May it fed on the flowers of
Ruta tuherculata, and as this plant began to go to seed
Ammi ma jus came into flower, and became for the
moment the plant on which eggs were most com-
monly laid. This plant was followed by Ducrosia
anethifoUa, which was not common, and probably
not an important food plant. While A, ma jus and
D, anethifolia were running to seed, Ammi visnaga
flowered and became an important food plant ; it
was in full flower in June after the first three were
quite dry. A fifth plant, Foeniculum vulgare, was
also found to be eaten by the larvae of P. mxichaon.
It seems then in Mesopotamia that the Swallow
Tail Butterfly has a regular succession of food
plants belonging to two unrelated natural orders
of plants — the Ruta to the Rue family, the others
to the Umbelliferae (Peile). One might argue from
this that if a caterpillar or other plant-eater pos-
sesses the power of living on a variety of plants it
may be able to survive under conditions which
would exterminate another caterpillar that could
only feed on one plant : in fact, that polyphagy
may be one factor determining the survival of
certain species in the desert.

In rather a similar way I noticed in Mesopotamia

RELATIONS OF ANIMALS AND PLANTS 125

I that a very large number of species of bees, fos-
sorial wasps, ruby wasps, and true wasps congre-
gated at whatever plant was in bloom. The

pHymenoptera could not afford to indulge their
preferences ; every species which was on the wing
might be taken now in a field of beans in flower,
a few weeks later at Zizyphus blossom, or Acacia
(Prosopis), or Lycium ; many of the species remained
on the wing during long periods, and a particular
species might frequent half a dozen different flowers,
each one exclusively for a short season. Such a
thing does not, I think, happen in lands where
flowers are commoner and the flowering season is
more prolonged.

The inroads upon the annual vegetation of the
larger grass-eating mammals, for instance, the
gazelles and hares in the Old World, are relatively
unimportant because the numbers of these animals
are limited by the scarcity of fodder during the
dry season. Spencer showed that adults of the
marsupial Phascogale cristicauda in Central Australia
were 40 per cent, to 60 per cent larger at the close
of a good season following rain and plenty of vege-
tation, than they were in a season in which rain
had been deficient. He beheves that this explains
the great variation in size which may be observed
among adults of other species of small marsupials.
It is only such small beings as the insects, with their
power of lying dormant in unfavourable seasons
and of rapid multiplication, which can take advan-
tage of the annual flora of the desert.

The plants of the second biological group, those

126 ANIMAL LIFE IN DESERTS

which store food in bulbs, tubers, and other struc-
tures underground, and are only above ground for
a short season, are probably of considerable impor-
tance to the fauna, but we have Httle actual know-
ledge on this point. Tristram, in speaking of the
deserts of Southern Palestine, says : " The vast
number of little rodents in apparent deserts is
explained by the nature of their food, which is
chiefly supplied by bulbous roots. The greater
part of the desert plants are tuberous or bulbous,
and after nine months of utter barrenness, the first
winter rains soon carpet the waste with a brilliant
spangling of bulbous flowers — crocus, iris, squiUs,
asphodels, cyclamen, and others. Their glory is
soon over ; but the large succulent roots remain,
retaining their moisture through the summer, and
affording abundant nutriment to the Httle bur-
rowers." Hart states that the wild boar wanders
far out into the semi-deserts of Beersheba in order
to root for bulbs, particularly those of the great
squill (Urginea, Fig. 26), and that in consequence
roots of this plant become quite difficult to obtain.
In the burrow of a Mole-rat (Spalax), in Egypt,
Anderson found a store of sixty-eight bulbs, but he
does not state the species of plant to which they
belonged.

It is natural that animals should be particularly
associated with plants of the third group, which
are above ground at aU seasons of the year, and
which supply food and water even at unfavourable
seasons to the creatures which can make use of them.
Many examples might be found of mammals and

RELATIONS OF ANIMALS AND PLANTS 127

birds which subsist largely or entirely on some
particular desert perennial. In Mesopotamia we
observed a very close relationship between the salt-
loving bush (Suseda) and a Dwarf Gerbille {Dipo-
dillus dasyurus). The Suaeda was a bush about
3 feet high and grew in salt patches in the desert :
a few bushes of Atriplex and Salsola were the only
plants found associated with it, and they were not
common. Several insects lived on the Suseda, and
the Dwarf Gerbilles Uved on any insects they could
catch, and on the succulent leaves of the plant.
They required no water in captivity, and in nature
they and the Suaeda bush lived far from the River
Tigris : there is little doubt that they were entirely
dependent on it, and the insects found upon it, for
food and water. The desert was flat and composed
of silt : it was devoid of any form of shelter except
the Suseda bushes, and among its roots the Dwarf
Gerbilles made their burrows. We may therefore
suppose that they derived from the plant not only food
and water but also protection from the foxes and
occasional jackals which existed in those parts of
the desert. So far as I know only one other
mammal, a hare {Lepus connori), occurred in the
salt patches of desert where the Suseda flourished.
It is natural that the animals should be few in a
place where only one plant grows and no water
can be obtained except from the plant, and it is
noticeable that three of the four mammals, the
fox, jackal, and hare, are active cursorial forms able
to wander far from the Suseda patch in search of
water and food.

128 ANIMAL LIFE IN DESERTS

In the same way it is stated that Pallas' Sand-
grouse {Syrrhaptes paradoxus) feeds very largely on
a salt-loving desert Chenopodiaceous plant, Agrio-
phyllum, in Central Asia.

Such close connection between the animal or
bird and the plant on which it lives is obviously
a potential danger to it. A severe drought, a fire,
a flood, or some other natural cataclysm, such as
is not uncommon in deserts, may exterminate bird
and plant together, at any rate over a part of their
range.

The plants which are most important as fodder
for domestic animals in deserts belong to those
perennials which live above ground at all seasons.
Sheep in the more arid parts of AustraUa depend
largely upon salt-loving succulents (Zygophyllaceae
and Salsolacese), particularly during periods of
drought, and in the drier parts of the southern
United States plants of the Cactus family are used
in the same manner.

I can recall only one instance of animals depen-
dent upon plants for water and not for food, and
that was observed in the hill country of Palestine,
which is certainly not desert, and barely falls within
our definition of semi-desert. However, in the
rainless summer, the season at which this obser-
vation was made, the country is extremely arid,
and the observation is, I think, suggestive enough
to warrant inclusion here. AH over the hills of
Judaea and Samaria there grows a genus of stout
thistles (Echinops) with spiny globular heads. These
flower in June and July when water is very scarce.

RELATIONS OF ANIMALS AND PLANTS 129

A large weevil {Larinus maculatus) and a Rose
Chafer {Protcetia libani) bite into the flower-heads
of this thistle, and feed on the interior, leaving an
open wound from which the sap continues to run.
This sap is drunk greedily by smaU bees, and wasps,
and ants, and would not be available to them
imless the weevil or chafer had first bitten into
the thistle. Such a method of obtaining drink is
not, of course, peculiar to desert cUmates ; the sap
which exudes from tree-trunks injiu*ed by Goat
Moth or other wood-borers, in Great Britain, attracts
butterflies, beetles, flies, and other insects.

Cases in which the animal depends on a plant
for food and water might be multiphed. The
relationship between Dwarf Gerbille and Suaeda, in
which protection as well as food and water is in-
volved, leads us on to another group of associations,
in which the principal or only bond between plant
and animal is shelter from climate or protection
from enemies.

Such an association was studied by Hartert in
the northern Sahara, a short distance south of
Biskra, in Algeria. He describes it thus : " After
leaving Bordj Saada the tamarisk bushes disappear
and a wide sandy plain covered with innumerable
stones extends to far beyond Bordj Chegga, where
the sand begins to prevail more and more. The
sandy plain, however, is not smooth or even, but
covered with countless little sandhills, the nucleus
of which is, or has been in each case, a bush of
Limoniastrum, Salsola, or other plant. Each iso-
lated plant arrests the sand that flies across the

130 ANIMAL LIFE IN DESERTS

plain with every wind, and winds are frequent,
and a miniature dune is formed ; the plant is partly
protected by the surrounding sand, but the latter
runs down from the top and threatens to suffocate
the plant, so that it strives for air and grows up-
wards, dying off at the lower end. Thus the hiUock
grows and grows and is crowned with a plant, imtil
the latter dies off and a little mountain remains.
These sandhills, hardened more and more in the
course of time, form the centres of all the animal
life except some of the birds. In these hillocks a
rodent, Meriones getulus, the Djerd of the Arabs,
makes its holes, which are used for nesting by
CEnanthe (Saxicola) moesta, and are sometimes in-
habited by the dreaded, deadly Asp {Cerastes
cornutus), the Lefa of the Arabs, and a beautiful,
harmless snake, Zamenis diadema. In these hillocks
one sees disappearing the pretty Hzard, Acantho-
dactylus scutellatus, and in them hides the nocturnal
Gecko, Stenodactylus guttatus. Also the beetles,
the common Anthia sexmaculata and Graphipterus,
and the rare and gigantic Anthia venator, as well as
some Tenebrionidse, disappear among these hillocks,
the former with wonderful swiftness. In this sandy
plain also, stony patches occur, Kke little islands
in the sea of sand, and on these is found the pale
Crested Lark (Galerida theUce deichleri). Along the
roads and on the sand we see another species of
Crested Lark {G. cristata arenicola), which it is
almost impossible to miss, while the first form is
easily overlooked when one does not know exactly
where to search for it; this was the reason why

RELATIONS OF ANIMALS AND PLANTS 131

we only discovered its real home on our way back."
Here the bond between the animal and the plant
is mainly that the animal obtains shelter from the
plant, or from the sand accumulated by the plant ;
but we know from other sources that the " Djerd,"
as well as other Gerbilles, are largely dependent
on the Limoniastrum leaves for food and water.

A most interesting case of the same nature, but
one in which the animals obtain shelter, but not
food or drink, from the plant, has been studied in
Arizona and California, by GrinneU and other
American naturahsts. The Saguaro, or Giant Cac-
tus {Cereus giganteus\ is a picturesque and very
interesting inhabitant of those deserts (Fig. 41).
It is an upright cylindrical plant, with very few
branches, and covered with spines ; it attains a
height of 30 or 35 feet, and a diameter of 2 feet
6 inches. Its fruit is attractive to many species
of birds, and according to Tuomey " nearly half a
hundred birds feed upon the fruit of the Giant
Cactus, the Hst including all our thrashers, wood-
peckers, finches, and pigeons." But the Giant
Cactus is not interesting only because birds eat its
fruit, and as it harbours few insects one might sup-
pose that there would be no close link between it
and the birds for the great part of the year. A
connection however exists, and it is a very close
one. To quote from Grinnell : " It is clearly
apparent that the critical feature of the saguaro
which prescribes its avian dependants is nothing
less than the favourable opportunity offered for
the excavation of safe retreats in its trunk : and

132 ANIMAL LIFE IN DESERTS

only the two woodpeckers are equipped for making
these excavations. So that, without the wood-
peckers to make holes, the other birds would be
no better off for the presence of saguaro." The
two woodpeckers to which he refers are the Gila
Woodpecker (Genturus uropygialis) and Mearn's
Gilded Fhcker {Colaptes chrysoides mearnsi). The
range of these woodpeckers is wider than that of
the Giant Cactus, and they have been found breeding
in trees of various species along the banks of the
California River. But wherever the Giant Cactus
grows the two woodpeckers are found, and found
more commonly than in other places, and when
it is possible the woodpeckers hew their nesting-
hole in this plant and nothing else. But for its
existence the birds would be confined to the river-
side growth of Cottonwood and willow; but as
they can excavate nesting-sites in the cactus they
are able to colonize desert areas where no other
large vegetation grows. Other parts of the same
deserts where there is no Giant Cactus have a
much poorer avifauna, for neither the woodpeckers
nor the birds which are dependent upon them are
foxmd there. The association between the Giant
Cactus and the two woodpeckers is closer because
the woodpeckers are strictly resident birds, remain-
ing all the year where they breed, and not wandering
far from that place at any season. As Grinnell
impUes in the passage which I have quoted, other
birds use the woodpeckers' nesting-holes, after the
woodpeckers have vacated them. The Elf Owl
(Micropallas whitneyi) is found exclusively in deserts

RELATIONS OF ANIMALS AND PLANTS 133

in which the Giant Cactus grows, and takes a dis-
used woodpecker hole for its nesting-place. It is
therefore dependent for its very existence on the
presence of a particular cactus, and either of two
particular woodpeckers. Less strictly dependent
upon the cactus and woodpeckers are a Screech
Owl (Otus asio gilmani), a Sparrow Hawk {Falco
s'parverius), a Flycatcher (Myiarchus c, cinerascens),
and other birds. None of these are confined to
the area inhabited by the Giant Cactus, but they
all inhabit that area, and within it they aU use old
woodpecker holes as nesting-sites.

Frequently a single trunk of the Giant Cactus
contains nests of one or other woodpecker, and also
of one of the birds which use the old woodpecker
holes. Honey-bees also use these excavations as
hives. One must remember that the number of
Hving creatures which eventually depend upon the
Giant Cactus includes the scavengers in the birds'
nests and bees' nests, the insects, few though they
may be, which devour it or frequent its blossoms,
and many others. AU these organisms depend upon
the growth of Cereus giganteus for their existence in
certain areas.

There are instances in which, contrary to the
general rule, the plants are dependent upon the
animals, and although these cases are not very com-
mon in deserts, a few may be mentioned. Botanists
teU us that there are two important agents, the
wind and the insects, by which the pollen of plants
is carried to the female flower, or female part of the
flower, which it is intended to fertiUze. In many

134 ANIMAL LIFE IN DESERTS

environments the insects fertilize more plants than
the wind does ; in deserts, perhaps because winds are
so common and blow without impediment among the
sparse vegetation, fertilization by wind is much
commoner than fertiUzation by insects : but the
insects, especially the bees, flower-eating beetles,
butterflies, and thrips, which are often so numerous
among the annual vegetation, no doubt fertiUze
certain species of plant, though at present we have
no clear knowledge on this point. One remarkable
fact is known : Loranthus acacice, a plant related to
the mistletoe, grows around the Dead Sea and in
the Lower Jordan Valley, as a parasite upon various
trees : it is almost certainly fertihzed by the Sun-
bird (Cinnyris osm\ which probes the tubular
blossoms with its long, curved beak.

According to Kobelt the Marmot {Arctomys bohac)
of Mongolia materially alters the character of the
vegetation round its colonies. The soil which is
thrown up round the burrows is suitable to special
plant types which are not common, and do not occur
together elsewhere in the steppe : round the colonies
of this rodent, and in no other place, these peculiar
" marmot gardens " are found. Bateson states that
in the very uniform steppes of Central Asia man and
his animals are a disturbing factor. Old camp-sites
can be seen from a great distance, because of the
patches of nettles which grow on them and not in
other parts of the desert.

The dispersion of seeds by birds and animals is
common to all parts of the world. Seeds which are
particularly suited to this means of conveyance are

RELATIONS OF ANIMALS AND PLANTS 135

generally provided with hooks with which they
entangle themselves in the feathers or hair of passing
creatures ; others are produced in a fleshy pulp,
which is eaten, and some at any rate of the seeds
pass unharmed through the intestines of bird or
mammal, or stick to its exterior until they are
deposited perhaps at a distance from the parent
plant. Numberless examples of seeds and seed-
vessels armed with hooks and spines could be quoted
from the flora of the Great Palaearctic Desert, especi-
ally from the annuals ; it is a common thing to
find such " burrs " in large numbers in the coats
of sheep, jackals, and even such smooth-haired
animals as gazelles and jerboas. Fleshy fruits are
not common in deserts, and many of those which
occur are so bitter or nauseating, or in other ways
unattractive, that they are shunned by the fauna.
Schimper states that jackals disperse the seeds of
CitruUus, presumably after biting the fruit, but I do
not think this is a common occurrence. The fruits
of many members of the Cactus family are sweet
and fleshy, though protected by spines. I have
already quoted Tuomey's remarks about the fruit
of Cereus giganteus and the birds which are attracted
to it ; Spalding adds that squirrels fatten on the
fruit of Echinocactus ; one is probably justified in
concluding that the seeds of the Cactus family are
largely spread by animals and birds. The date-
palm {Phoenix dactylifera) is entitled to a place on
the Hst, though palms which produce fruit edible to
man do not exist wild.

Dates in Mesopotamia are eaten greedily by

136 ANIMAL LIFE IN DESERTS

several birds, but by none more than by Hypocolius
ampelinus. These instances must not be supposed
to imply that fleshy fruits are common in deserts ;
the reverse is the case.

Animals serve the plants by distributing their
seeds, but they do immense harm to the vegetation by
devouring plant and seed ahke. The deserts of the Old
World support large numbers of domestic goats, sheep,
cattle, and camels, and of wild gazelles, antelopes,
and hares, and these animals Hve by browsing shrubs
and herbs. In the neighbourhood of a bedawin
encampment or an Arab village or a frequented
track it is almost impossible to find an untouched
plant of any kind. Cannon observed in Algeria
that the Mzabite cemeteries, in which the domestic
animals are not allowed to graze, form a place of
refuge to plants which otherwise do not exist at all
near the haunts of man. It is frequently stated that
thorns (page 62) are produced as a defence against
these browsing animals, and this explanation may be
true in some places, but certainly does not fit the
facts very generally. In favour of the defensive
theory is the fact that in the Southern United States
and in parts of Australia, where species of Opuntia
(" Prickly Pear ") are used as food for sheep and
cattle, only the thorny species can be successfully
grown. If the thornless species are planted they
must be protected by fencing against the grazing
animals, and it is actually cheaper to grow the
thorny species and to destroy the thorns by fire,
when the plant is required for the stock, than to
protect the thornless ones with fences. It is a fact

RELATIONS OF ANIMALS AND PLANTS 137

also that certain plants which are without thorns
spring up in the midst of a thorny bush of another
species : in the Algerian Sahara the Terebinth or
Betoum tree (Pistacia) is shielded by the Zizyphus,
and in the Indian desert the Zizyphus protects the
grass Andropogon in a similar manner. It is
generally supposed that the Terebinth and Andro-
pogon are protected from grazers by the Zizyphus,
but one must remember that any plant which suc-
ceeds in estabhshing itself tends to shelter the soil
around it, and to hold together the particles of soil
if they are light and inclined to blow away. One
well-established perennial plant mitigates the cUmatic
conditions, and becomes the centre of a group of
other plants of several species, and this wiU happen
whether the perennial is thorny or not. It is possible,
therefore, that the shelter which the Zizyphus affords
from wind and heat is more important than the pro-
tection which it gives from grazing animals. Against
the theory that thorns afford protection from grazing
animals one may advance the fact already quoted
that near human habitations, or frequented tracks,
aU desert vegetation, whether thorny or not, is
stunted and deformed, or exterminated, because of
the animals which graze upon it. From Central
AustraHa we have Baldwin Spencer's evidence that
the camel can eat every plant, from the spiny Acacia
farnesiana to the juicy Claytonia. In the semi-
deserts of Palestine camels prefer some of the more
thorny shrubs, such as the Caper (Capparis), to others
which are almost unarmed, but which are beheved
to be bitter, or nauseating by reason of taste or

138 ANIMAL LIFE IN DESERTS

smell ; but Hart noted that they would eat Daemia,
a very milky Asclepiad. I have seen goats at Jericho
climbing up to browse on Zizyphus twigs though
the spring herbage was up to their bellies.

Furthermore, thorniness is most highly developed
in the most arid deserts, exactly where large grazing
animals are rarest, and the plants of the American
deserts are on the whole more thorny than those of
the Great Palsearctic Desert, though wild grazing
animals are rare in the American deserts.

The majority of the cacti are covered with long,
straight thorns, which mice use as if they were
rungs on a ladder ; the fruits (e.g. in Opuntia) carry
small tufts of minute barbed hairs, which are easily
detachable and very sharp ; these are thickly set
on the fruit, and it might be supposed that they would
form an efficient defensive mechanism, but this is
far from being the case. In the American deserts,
in which these plants are native, the squirrels and
mice eat the fruits in great quantity. In the Old
World, where Opuntia is an introduced plant, the
rodents have learnt to climb the plants and steal
the seeds. At Jaffa two species of the genus are
cultivated : the fruit of one is eaten by man ; that
of the other is opened by Gerbils (Gerbillus allenbyi),
which gorge themselves and leave very few seeds
to germinate. With the spiny fruit of Opuntia we
may contrast the native and apparently defenceless
gourd of Citrullus colocynthus, the Colocynth, which
is not eaten by rodents or ruminants or jackals,!
apparently because it is bitter and violently]
purgative, and the Water Melon (C vulgaris), which

RELATIONS OF ANIMALS AND PLANTS 139

is even more defenceless, for it is neither bitter nor
purgative, and yet it frequently escapes from
cultivation and thrives without protection from man
in India, Palestine, and doubtless other places.

The conclusion to which these facts lead me is
that thorns were not developed as a defence against
grazing animals or rodents, and that they do not
usually act in that way : I freely admit that they
occasionally may exercise such a defensive function.
They were probably developed in the first place as a
response to the dry atmosphere.

CHAPTER VII
THE COLOURS OF DESERT ANIMALS

There is no doubt that the colour of desert animals
is in some way the result of the conditions under
which the creatures hve, because it is quite char-
acteristic of them, and not of animals from other
types of country. Whether this colour is due to
chmate or is protective we do not know, and I
propose first to discuss the facts and then to examine
a theory that has been brought forward to explain
them.

The majority of the animals which Hve in deserts
are coloured buff, or sandy, or reddish-grey, and as
plants are scanty and only very rarely cover the
surface of the earth, we may say that generally the
desert fauna resembles the ground on which it lives.

Furthermore, the colour of the typical desert
creature is imiform, without remarkable pattern on
the upper surface. A few birds, such as the Horned
Lark (Eremophila alpestris hilopha) and the Cream-
coloured Courser {Cursorius gallicus) and a few
Gazelles among the mammals, have blackish mark-
ings on the head, but such a pattern is exceptional.

Though the dorsal surface of most desert animals
appears to a careless glance to be of one colour,

140

THE COLOURS OF DESERT ANIMALS 141

when a specimen is examined closely it will often
be found that the general unicolorous effect is
produced by fine mottHng. In the Palsearctic
region we have many examples of this ; among the
birds the Egyptian Nightjar (Caprimulgus cBgyptius),
many Sandgrouse (Fig. 34), especially females, Hey's
and See-See Partridges (Ammoperdix) ; among the
mammals several foxes and gerbik, in which a
general sandy tone is produced by the presence of
black hairs or black-banded hairs among the pale
hairs ; many moths, especially Geometridse, in
which a unicolorous appearance is produced by fine
and inconspicuous banding or mottling ; in fact,
fine vermiculation, producing a general impression
of " self -colour," is common.

In many desert mammals the under-surf ace is very
pale or quite white. It is a fact that desert species
and sub-species differ from their near relatives from
other environments just as much in their pale
ventral surface as in their buff or sandy backs.
Moreover, the pale ventral area is often more
enlarged up the flanks of a desert mammal than it
is in its relatives from other environments. This
paleness of parts of the animal which cannot normally
be seen extends even to the sole of the feet : Sumner
states that "the soles of the feet of desert deer-mice
are nearly or quite lacking in pigment, while those
of mice from the more humid coastal regions vary
from purplish to nearly black."

This type of coloration is found in all groups of
animals which inhabit deserts ; in spiders and
centipedes and wood-lice; in moths, bugs, beetles.

142 ANIMAL LIFE IN DESERTS

bees, flies, grasshoppers, and wasps ; in many lizards,
and snakes ; in many birds of many different
families, larks, finches, warblers, owls, partridges,
nightjars, waders, and others ; in many mammals of
many groups, rodents and insectivores, and bats
and ungulates and marsupials. In fact, I cannot
quote a single group of animals which lives in the
desert and which does not furnish examples of this
general truth. The only apparent exceptions are
to be found in certain groups of beetles and other
small Arthropods which Hve their whole Hfe below
the surface of the ground.

This type of colour and of pattern which we have
come to recognize as characteristic of the fauna
of deserts is not only widely distributed in the animal
kingdom, but widely spread over the world. In
any desert, in any of the five continents, you will
find these sandy or buff birds and mammals and
insects, and you wiU not find them in numbers in
any environment which is not desert or semi-desert.

Further, it may be stated that desert-dwelling
animals are not coloured isabelline, or reddish buff,
or greyish, indiscriminately ; for there is often a
very close similarity in colour between the creature
and the soil of the particular type of desert on which
it lives. Thus, Lucas and Frost, in discussing the
lizards collected by the Horn Expedition in Central
Austraha, refer to the " presumably protective colora-
tion of the species of diurnal habits. Many of these
exhibit a very marked general rustiness, or even
bright redness, in their general colouring, which is
quite wanting in the forms met with in the South

THE COLOURS OF DESERT ANIMALS 143

and East, and which agrees well with the colour of
the red sands upon which they were captured.''
These authors also quote Prof. Spencer's field notes
made on the same expedition, with regard to an
Agamid Hzard {Amphibolurus barbatus) : " On open
country to south of Charlotte waters, a general
yellow-brown colour — similar to general colour of
ground, with withered grass, etc.," which is con-
trasted with the series collected "at Crown Point,
where plenty of red sand was, a peculiarly brick-red
colour much resembhng the colour of the sandy hills
close to the camp where it was found." It is
particularly interesting to find that this species so
closely resembles two different types of desert soil,
for it is widely distributed in AustraHa, and by no
means speciaUzed to a desert environment. The
birds, too, furnish the most beautiful examples of
species coloured so as to be well-nigh invisible
among their native stones so long as they remain
motionless. One of the Crested Larks {Galerida
theklce) is represented by a dark race (G. t harterti)
in the northern parts of Algeria, which are not
desert ; in the semi-deserts which fringe the Atlas
Mountains southwards this is replaced by a paler
race {G. t. hilgerti) ; in the Northern Sahara itself
a still paler race is found (G, t, deichleri), which " is
so wonderfully adapted to the soil that it is easily
overlooked if the birds do not happen to be on the
wing or singing " (Hartert). Between Laghwat and
Ghardaia a reddish form (G. t, carolince) of this
species is found, and its distribution corresponds
fairly closely with the reddish stony desert. The

144

ANIMAL LIFE IN DESERTS

colour and distribution of these races finds its
parallel in the hares, Lepus pallidior, which is pale
and greyish and is found along the south side of
the Atlas Mountains, and L. whitakeri, which is
reddish sandy, and is found in the country round
Ghardaia. Meinertzhagen has studied certain races
of another species of Crested Lark {Galerida cristata)
and arranges them thus, beginning with the darkest
and ending with the palest.

Race.

SoiL

Locality,

Nigricans .

Black alluvial

Central Egyptian Delta

Maculata . .

Dark alluvial with a

percentage of sand

Cairo, Helwan

Meridionalis .

Dark brown, often red

Crete

Dark brown

Cyprus

Cinnamomina

Reddish

Beirut

Brown

Haifa

Zion . . .

Brown to pale brown

Damascus, Tiberias,
Jerusalem

Brachyura

Pale brown and sand

Suez, Gaza, Sollum,etc.

He quotes also the mean relative humidity and
the mean rainfall of the locaUties, both for the year,
and for the months April and May, when the birds
are breeding. He concludes that " Crested larks
are influenced in the colour of their plumage by
protective resemblance to the soil on which they
live, and that neither humidity nor rainfall has any
effect on their plumage. This same influence seems
to affect nearly all ground-birds which more or less
live in the open, such as Ammomanes, Alcemon^
CEnanthe deserti, Eremophila, Alectoris, Pterocks, etc."

THE COLOURS OF DESERT ANIMALS 145

For reasons which I shall give later I am not
convinced that the resemblance of birds to soil is
" protective," if by that word it is implied that the
resemblance affords protection from enemies, but
let us accept it that there is a close similarity between
the colour of the bird and the colour of its native
soil.

It is also interesting that in the first plumage
these Crested Larks show very much the same
differences in shade as do the adults of the same
sub-species. The feathered young of G, c. brachyura
is, for instance, paler than that of G, c, nigricans,
and both of them are very much paler than specimens
of G. c. cristata, the Central European race.

A somewhat similar case is that of the Houbara
Bustard. The typical sub-species {Chlamydotis u.
undulata) inhabits the Sahara and Southern Morocco,
and is of a mottled sandy colour, which accords
well with the pale and sandy soil on which it Hves.
In the Eastern Canary Islands (Fuerteventura and
Lanzarote) the sub-species C, u, fuerteventurce is
found : it differs from the typical sub-species in
the speckling and mottling of its upper surface
with black ; it harmonizes very closely with the
lava-strewn wastes of these islands, and the typical
pale race would be extremely conspicuous upon
them. Accurate information with regard to the
humidity of the air and the rainfall of these islands
is lacking, but Bannerman attributes the blackening
of the island race to its existence upon the blackish
lava.

It seems to be agreed among American zoologists

146 ANIMAL LIFE IN DESERTS

that mice, wood-rats, and other small mammals
which inhabit areas of blackish lava as well as other
parts of the desert are often darker on the lava than
elsewhere. It is fair to mention that this has
recently been controverted by Sumner, who has
shown that in some cases, at any rate, the darker
colour may be due not to living on lava, but to
differences in other environmental factors, such as
rainfall. In the case of one animal (the deer-mouse,
Peromyscus crinitus), he was able to show that if
long series of this mouse living on black lava and on
" pale grey, buff, and pinkish " rock were compared,
no difference in tone could be detected either by eye
or by photometer.

Other cases occur in which the resemblance of
animals which are, broadly speaking, " desert-
coloured " to their particular type of desert, is by
no means very close. I remember obtaining four
species of mammalia at Qazvin in North- West
Persia : the local fox was greyish sandy with a
reddish saddle ; the hare was pinkish buff ; the
gerbil {Meriones hlachUri lycaon) was yellowish buff ;
and the dwarf hamster (Cricetulus) pure pale grey
without any trace of yellow or buff colour. All
these occurred on the same ground, and any one of
them was a good example of " desert coloration,"
but none of them resembled the exact shade of the
soil at all closely.

In Mesopotamia downy young of the Sandgrouse
Pterocles senegallus and P. exustus have been obtained
in the same type of pebble and clay desert, but they
differ widely both in pattern and colour.

THE COLOURS OF DESERT ANIMALS 147

Grinnell has recorded a similar phenomenon.
Speaking of " conies " (Ochotona), by which an animal
very different from the bibHcal cony or hyrax is
meant, he says, " as elsewhere, the conies in the
white momitains live in rock sUdes and broken-up
rock out-crops." Two colours of rock occur in this
range, a blackish or dark red ' shale,' and a white
or greyish white granite. There are extensive belts
purely of one or the other kind of rock. Our party
took pains to shoot conies from each colour of
ground, keeping notebook record of where each
specimen was shot. I am unable to detect any
difference in colour between animals shot from white
granite and those from dark ' shale.' "

Speaking of the Roadrunner {Geococcyx californi-
anus), a large, ground-loving Cuckoo found in
California, he remarks that "it is, of course, a
remarkable exception if the Roadrunner, a terrestrial,
permanently resident bird of all the areas it inhabits,
should not show some geographic colour pecuHarities.
Lideed, it is all the more strange that it does not show
conspicuous differences in colour tone in the arid
and subhumid areas it occupies, when we observe
the remarkably different colour tones exhibited by
the thrashers, towhees, spermophiles and jack
rabbits of the same areas, these also being terrestrial
animals. The Roadrunner's failure to conform to
the rule offers a problem for those who would explain
animal coloration whoUy on the ground of physio-
logical response to meteorological conditions, irre-
spective of adaptive value."

Certain desert insects attain a silvery or sandy

148 ANIMAL LIFE IN DESERTS

appearance by being clothed with hairs of that
colour ; many of these insects settle rarely or never
on the desert soil, so that their case deserves special
consideration. The phenomenon is found in many
bees, wasps, and fossors, and in at least three
famihes of flies (Bombyliidse, Nemestrinidae, and
Tabanidae). That is to say that it has been evolved
on a number of separate occasions to suit the particu-
lar needs of insects that fly or hover over deserts.
Morice was, I beheve, the first to call attention to it
in Hymenoptera, remarking that " no one, I should
think, who has collected in the deserts of Algeria,
Egypt or Palestine can doubt that the very pale
colours and shimmering silvery or golden pruinosity,
so common in aU groups of Hymenoptera in such
locahties, and practically there only, are cryptic
characters, rendering the insects which possess
them inconspicuous and almost invisible among the
guttering sand and pale vegetation which they
haunt. Here at least, contrary to the rule laid down
by Wallace, we have stinging Hymenoptera coloured
so as to resemble, or at any rate so as not to con-
trast with, the inanimate and vegetable substances
which normally surround them." I have quoted
his words because they describe the facts excel-
lently ; his suggestion that the colours are " cryp-
tic " is a topic to which we shall return later. A
similar condition prevails in the gad-flies (Tabanidae),
many species of which from Mesopotamia and
South Palestine are clothed with down of a pale
tawny colour. This is remarkable, because the gad-
flies rarely settle on the ground or on rocks except

THE COLOURS OP DESERT ANIMALS 149

at night, and spend most of the daylight hours
visiting flowers or sucking the blood of the larger
animals. Certain flies of the famiHes BombyUidae
and Nemestrinidae exhibit the same type of colora-
tion, though they spend their time at flowers or
hovering in the air : they do not rest on the soil
which they so closely resemble in colour.

We find, then, that most of the animals which live
in deserts are coloured buff or sandy or pale grey ;
bold pattern is rare ; this type of colour is exhibited
by animals of nearly every group, and is prevalent
in the deserts of every continent. It is even char-
acteristic of some insects, not closely related to one
another, which spend the hours of daylight in the
air or on flowers and not on the surface of the
desert. As to the effect of these colours upon the
human eye it must be acknowledged that the
prevalent buff and sandy colours of desert animals
do render them extremely difficult to detect, unless
they move. This is probably as much due to their
immobility as to their colour. Every naturahst
who has ever visited the desert has noticed this,
and it is true of all the manifold forms of life which
exhibit these colours. The most remarkable exam-
ple that ever came to my notice was in Baghdad,
Mesopotamia, in September. There was a small
patch of ground of perhaps an acre, walled off but
not at that season cultivated. In it one could always
be certain of flnding at least a score of Egyptian
Nightjars {Caprimulgus cegyptius), but though the
ground was absolutely bare, and though I visited
the place repeatedly, I never succeeded in detecting

150 ANIMAL LIFE IN DESERTS

a Nightjar before it flew, and this in spite of the
comparatively large size of the bird. We must
admit it as a fact that the prevalent colour of desert
animals does render them most difficult to see so
long as they remain motionless.

There is only one important exception to the
generaHzation that desert animals resemble in colour
the soil on which they live, but it is a most remark-
able one ; in many deserts a number of the indigen-
ous animals are black. This is not commonly
known, but is none the less fact. Speaking generally,
it may be said that any desert creature which is
not coloured Hke its surroundings is black, for
bright greens and blues and reds and yellows are
very rare ; and though black animals are not a
dominating element in the fauna, they are suffi-
ciently numerous to be noticeable in many places
in the Great Palaearctic Desert. The most remark-
able group of black inhabitants of deserts are the
Tenebrionidae, a family of beetles. Members of
this family, to which the meal-worm (Tenebrio) and
the Cellar Beetle (Blaps) belong, are found in a great
variety of environments in nearly aU parts of the
world. The majority of them are black, and
nocturnal ; the habits and food of these insects are
very imperfectly loiown, but it is beHeved that the
larvae and adults of most feed on dried vegetable
matter, and refuse generally ; possibly their abihty
to live on dry food has enabled them to invade the
arid areas of the globe. Whatever be the reason, the
Tenebrionidae have proved successful in colonizing
arid countries, and, as the following Hst shows, aU

Fig. 42. — Typical Black Diurnal Tenebrionid Beetles of the Great Pal^arc-
Tic Desert (x 4^). A. and B, Adesmia ulcerosa; C and D, Pimelia
angulata. (E. Terzi.)

THE COLOURS OF DESERT ANIMALS 151

the large deserts of the world are inhabited by one
or more of the many sub-famihes into which these
insects are divided : —

Sub-family. Desert inhabited.

Erodiinae ..... Palaearctic

ZophosinsB „ and African

TentyriinsB „ „ „

Adesmiinae ..... ,, j, »

Eurychorinae ..... South African

Cryptochilinae ...... „

Molurinse ...... „

Sepidinse ..... Palaearctic and African

Akidinae ......

.... ,,

Pimeliinae .....

j> )> }>

Blaptinae ..... „ ,j „

Eleodinae . . . . . American

Praocinae ..... ,,

Coniontinae ..... „

Adaliinae ..... Australian

(K. G. Blair in litt.)

Blackness, as I have said, is characteristic of the
Tenebrionidae. The desert environment has not
affected them, for in all the deserts in which they
occur the majority of species remain black. As
many of them are nocturnal, and as they shelter
by day under rocks, this is not at first sight remark-
able, but it is very remarkable that others have
acquired a habit of wandering over the naked ground
by day, and that these retain their uncompromising
black colour. Examples familiar to the traveller
in any of the deserts of Algeria, Egypt, Palestine or
Persia are the genera Adesmia and PimeUa (Fig.
42). These are large black active insects, and they
are a dominant part of the fauna of these countries
in winter, spring and early summer. Their activity
is strictly diurnal, for they do not take refuge from

152 ANIMAL LIFE IN DESERTS

the midday sun, but retreat under stones at night
and during cold weather. ^ As these insects are so
numerous and so visible one naturally wonders how
they protect themselves from insect-eating birds
and lizards. It appears probable that they are to
some extent saved from destruction by their size
and their hardness : this is an inadequate protection,
for the late G. Storey shot a young black and white
Wheatear (species ?) in Wadi Hof, near Cairo, and
found that it was stuffed with Adesmia, and Radde
recorded long ago that the Red-footed Falcon
{Falco vespertinus) eats Blaps and PimeHa on the
Simferopol Steppes in April.

The anomaly of the black colour and diurnal
habits of these insects is heightened by the fact that
some desert Tenebrionidse are dull brown, others are
black and hairy, but they cover themselves with an
earthy or dusty coating which is difficult to remove ;
these inconspicuous Tenebrionidae are nocturnal
insects, and it is difficult to see that their camouflage
is of value to them.

Black members of the Chafer family of Beetles,
among them the famiUar " Scarab " of Egypt and
other countries along the Mediterranean Httoral,
occur in many places in the Great Palaearctic Desert,
but they are neither so common nor so character-
istic as the Tenebrionidae. Among the flies there are
several species of Bombyhidse in the Great Palse-
arctic Desert, which are black, or predominantly
black. Fig. 43 shows a member of (a) the Bom-

^ This statement is probably true of all species of Adesmia
and of many Pimelise (e.g. P. angulata, Fig. 42) : other members
of the genus are nocturnal.

Fig. 43. — ^Typical Black Diurnal Flies, from Palestine, belonging to differ-
ent SUB -FAMILIES OF THE BoMBYLiiD^ (x 4^). A, Bombylius fuscus (Bom-
byliinse) ; B, Hemipenthes sp. (near H. velutina), (Anthracin^). (E. Terzi.)

THE COLOURS OF DESERT ANIMALS 153

byliinse, and (b) the Anthracinse, a sub-family in
which this phenomenon is quite common.

In the Algerian Sahara among the numbers of
active black Adesmia one may frequently capture
a large Long-horned Grasshopper, black and shiny,
with red processes on the thorax. This insect is
Eugaster guyoni. In contrast to the active Adesmias,
it is a very sluggish insect and its hindlegs are not
specially lengthened and strengthened for jumping
as they are in nearly all its relatives. Further, we
may suppose that Adesmia and the other diurnal
Tenebrionidse are black by inheritance, and that
they have retained the family's colours not because
it was directly advantageous, but because it was not
disadvantageous. No such reasoning can be appUed
to Eugaster, which belongs to a family in which
shiny blackness is extremely rare : we are therefore
left to wonder at its assumption of this colour and
at its abrogation of the power to jump. Eugaster
is extremely conspicuous and deliberate in its
motions ; when it is handled it pours forth a copious
brown oily secretion, and it is tempting to suppose
that this protects it from insect-eaters ; we have
absolutely no evidence that this is the case.

Among the Short-horned Grasshoppers (Locus-
tidse or Acridiidae) there is an interesting species,
CalUptamus coelesyriensis, which ranges from Pales-
tine to Turkestan. In Palestine it occurs in semi-
desert country among withered annual vegetation in
the months of May and June. One common form
is very dark chocolate brown all over, except that
the ventral surface is slightly paler. I have nearly

154 ANIMAL LIFE IN DESERTS

always found it associated with much greater num-
bers of a pale buff form of the same species ; inter-
mediates between this and the chocolate form do not
occur in my experience. It is remarkable that two
varieties of one species, living in identical environ-
mental conditions at the same season of the year,
should be so differently coloured, the common form
resembling the surrounding stones and dead herbage
in colour, as do nearly all other members of the
family, the rarer form being nearly black and very
conspicuous. Another member of the same family
{Poecilocerus bufonis) in Sinai is dimorphic in a
similar manner.

In most parts of the Great Palaearctic Desert,
birds which are mainly or entirely blaick are found.
Excellent examples are afforded by the Ravens and
by a large number of species of black and white
Wheatears and Chats (Saxicola). The latter range
right across the Great Palaearctic Desert, from Rio
de Oro and Morocco to Turkestan, Sind and Raj-
putana. Inside the belt of desert and semi-desert
they are abundant both as species or as individuals,
and outside it they are rarer, and occur for the most
part as stragglers. Blackness is not an ancestral
colour for Wheatears and Chats, and is quite excep-
tional among them. One can trace a progressive
series among the desert members of the genus,
showing the gradual replacement of buff by white,
and then the replacement of the white by black.

In some species the blackening has proceeded
further in the male than in the female, in other
species both sexes are equally black. It appears

THE COLOURS OF DESERT ANIMALS 155

therefore that these birds have evolved their
blackness because in some way it fits them to a desert
existence ; in this respect they resemble Eugaster
guyoni and the dark form of Calliptarmos code-
syriensis. This is the more remarkable because
within the limits of the same genus (Saxicola)
there are birds which inhabit the same deserts and
which are coloured like the soil on which they live ;
examples are the Isabelline Wheatear {8. isdbeU
Una) and the Desert Wheatear {8. deserti), both of
which are widely distributed in the Great Palae-
arctic Desert, and occur side by side with various
black and white congeners. The habits of the black
and white Wheatears closely resemble those of the
other members of the genus, that is to say that they
are wary birds, given to perching on upstanding
rocks and, at any rate to my eyes, easy to see when
they are sitting still, and extremely conspicuous
when they move.

Among the reptiles there is one species which
becomes increasingly black beneath as its habitat
becomes more and more strongly desert. Hartert
has recorded that the spiny-tailed Hzard ( Uromastix
acanthinurus) of Biskra, El Kantara, and other
places in the northern part of the Algerian Sahara
is replaced farther south in the Mzab country by a
form which is much blacker on its ventral surface,
and that this in turn is replaced in Tademait and the
central Sahara by a form in which the males are quite
black, and the females nearly so, aU over the under
surface of the body and the tail. This very remark-
able case can scarcely be grouped with those which

156 ANIMAL LIFE IN DESERTS

we have already considered as the increased black-
ness of the more desert forms of this species is con-
fined to the invisible ventral surface. ^

I can find few records of the occurrence of black
diurnal animals in any desert outside the Palsearctic
region : it is possible that black animals occur and
that no one has called our attention to them. It is
interesting to notice that Merriam refers to the
Tenebrionid genera Eleodes and Asima as common
and characteristic in the Painted Desert, in America.
Hudson speaks of Galictis barbara, a " quaint-looking
weasel, intensely black in colour, and grey on the
back and flat crown"; this animal is diurnal and
hunts in companies on the pampas of La Plata. In
the same country is found Didelphys azarce, a black
and white oppossum : this animal is also diurnal.
It is, of course, possible to suppose that these two
totally unrelated conspicuous diurnal predatory
animals exhibit " warning coloration," a topic too
large to be considered here.

I have summarized the facts ; let us now see
whether they are capable of explanation. Many of
us, during our childhood, were taken to the Natural

1 Among the Amphibia and Reptiles which inhabit deserts
there are species which develop brilliant colours in the wet season
in such a way that they become extremely conspicuous. This
brilliance reaches its climax after pairing has taken place, and
is common to both sexes of the frog or lizard concerned. For
details consult C. L. Camp, Notes on the Local Distribution and
Habits of the Amphibians and Reptiles of South-Eastern California
in the Vicinity of the Turtle Mountains, Univ. of California
Publications in Zoology, XII, p. 511 (Aug. 12, 1916), and Baldwin
Spencer, Report on the Work of the Horn Scientific Expedition
to Central Australia, Part I, pp. 26, 27 (1896).

THE COLOURS OF DESERT ANIMALS 157

History Museum in Kensington, and shown the large
case which illustrates desert hf e. We remember the
sandy rocks, the sparse dry vegetation and the birds,
beasts and reptiles all coloured so that they were
inconspicuous. We did not reaHze that they were
inconspicuous, at any rate in part, because they
were motionless, and that about half the creatures
in the case were strictly nocturnal. We were told
that the animals were so coloured as a protection
from their enemies, and most of us have grown up
without ever critically examining this statement, so
that the theory of protective coloration is still widely
accepted by people who are not strictly scientists,
but are very deeply interested in biological problems ;
the time has come to examine it very closely. This
theory presumes that there are predaceous creatures
from which the animal must be protected, or else
that the animal is itself predaceous and that its
colour enables it to stalk its prey with success ; the
theory presumes also that the protection given is
actually effective under natural conditions in the
open desert. One asks at once from what enemies
the desert creature needs to be protected. Admit
that the moths, grasshoppers, mantids, spiders,
and other smaU organisms are preyed upon by
insectivorous birds and reptiles, and suppose that the
colour of these small animals gives them some
measure of safety ; the supposition is not based on
accurate knowledge, but it is not unreasonable.
Now, what are the enemies of the larger "pro-
tectively coloured " birds, the Sandgrouse (Pterocles)
and Courser (Cursorius) ?

158 ANIMAL LIFE IN DESERTS

Falconers say that as a general rule trained
Peregrines and Shahins cannot capture these birds
except by chance, and that the ordinary desert
Falcons, the Sakers and Laggers, are less swift than
the Peregrines. It would seem, then, that the
Coursers and Sandgrouse are protected from Falcons
more by speed than colour. I know of no other
predaceous animals which hunt by day and which
may be supposed to chase Sandgrouse or Courser.

The real enemies of these birds are probably cats
and foxes and possibly jackals ; these aU hunt by
night and by scent, so that the colour of the bird
motionless in a dim light can hardly have a protective
value to it.

Now, let us consider the predaceous birds and
animals — first those of diurnal and then those
of nocturnal habits. The supporter of protective
coloration supposes that they are coloured like the
desert in order that they may more successfully
stalk and seize their prey, that is to say that their
colour effaces them. This ingenious explanation
fails to cover the facts. The Merlin is fairly famihar
to many of us as a small hawk, widely distributed in
Europe and Northern Asia. It feeds largely on small
birds and hunts on the wing ; any colour and pattern
which is to prevent the small birds from seeing it
should therefore be on the imder side of the bird.
As a matter of fact, the ordinary western form of
Merlin {Falco columharius regulus\ which does not
breed in deserts, winters, among other places, in the
deserts of Algeria, Tunisia and Egypt. Farther
East, however, there is a race {Falco columbarius

THE COLOURS OF DESERT ANIMALS 159

pallidus) which breeds in the deserts and steppes of
Central Asia ; this race is desert-coloured, being a
very pale and dehcate blue-grey above, and paler
beneath than the western race. The western
Merlin, which is not desert-coloured, is well able
to find a Hving in the deserts in which it winters ;
on the supposition that the Merlin requires effacing
coloration, why is it necessary for the eastern race
to be coloured very pale, and particularly why should
the colour of its upper surface be paler than that of
the western race ? A good parallel is afforded by
the larger falcons. The Peregrine {Falco peregrinus),
which is not a desert-breeder and is dark iron-grey
above, winters in many of the Great Palsearctic
deserts ; in these regions one finds also the Saker
Falcon (Falco cherrug) and the Lanner Falcon
{F. biarmicus), which are pale desert-breeders. One
cannot see that the desert species have any advantage
over the Peregrine during the months during which
they five side by side.

With the Falcons the theory of protective colora-
tion, or rather of effecting coloration, fails to cover
the facts, but the effacing colour of other predaceous
animals does help them to catch their prey. In the
CaHfornian deserts near the Turtle Mountains there
exists, according to Camp, a Rattlesnake (Grotalus
cerastes) which is coloured so that when it Hes
buried in sand flush with the surface it is well-nigh
invisible. Invisibihty, or some close approach to it,
really is attained, and the snake and the Hzards
which form its prey are active by dayhght at a
time when the value of colour as an effacer must

160 ANIMAL LIFE IN DESERTS

be at its highest. Instances such as this are few,
and the theory of protective or effacing coloration
which explains them well enough cannot be extended
generally.

In the case of nocturnal beasts and birds of prey
it is still more difficult to explain colour as an effacer,
because even by moonlight colour hardly exists, and
differences between shades of colour are not appre-
ciated. All the same, there is a large group of desert-
coloured, nocturnal, predaceous forms, some hke the
owls hunting by sight, others Hke cats and jackals
and foxes by scent. All are pale in colour, and from
numerous examples, occurring in aU deserts, I choose
the following. Thomas has recently described a
Caracal from Asben in the South Central Sahara. It
differs from all known Caracals in its "exceptionally
pallid coloration and silvery ears." It is "a desert-
coloured form with whitish ear-pencils." Among
the birds the Eagle Owl (Bubo bubo) is a wide-ranging
species able to support itself equally in the forests of
Scandinavia and the steppes and deserts of Persia,
Transcaspia and Egypt. A large number of sub-
species have been described and they form a most
interesting gradation from the large dark forest
birds of Europe and North- West Asia to such small
and pale desert forms as Bubo b, aharonii in Southern
Palestine ; B. b. ascalaphus in North Africa and
Egypt ; B. b. turhomanus in Transcaspia, East
Persia and Turkestan, and other forms.

There is, of course, a stiU larger group of animab
which are preyed upon and which are nocturnal.
Nearly aU the Jerboas and Gerbils of the Old World,

THE COLOURS OF DESERT ANIMALS 161

and their counterparts in the American deserts and
Australia (pages 74-80), are strictly nocturnal, and
one may weU question whether their beautiful sandy
tints have much protective value. By moonlight, to
the human eye they appear nearly white and rather
conspicuous. Most of them, it should be remem-
bered, are very strictly nocturnal : Jerboas {Jaculus)
and Dwarf Gerbils (Dipodillus) may occasionally be
seen when the dayhght has nearly gone, but many
other forms never come above ground until night
has definitely faUen. In the summer and autumn
of 1919 I was camped for four months outside
Qazvin in the semi-desert of North- West Persia. All
around us were the burrows of the Gerbils {Meriones
blackleri lycaon and M, erythrurus), but never once
did I see either of these animals by dayhght, either
in the dawn or after sunset : every night I was in
the desert between 8 and 9 p.m., and I always saw
Gerbils crossing the beam of my lamp. Without
a lamp I found it impossible to see them except when
the moon was bright, and then they appeared white
and conspicuous. Devout supporters of the theory
of protective coloration claim that animals, both
predators and prey, are rendered iaconspicuous even
at night, perhaps by moonlight, by their pale colour ;
the claim seems to me to be more ingenious than
probable, but I cannot disprove it. The whole
question of visibiHty at night, with or without moon,
is beset with difficulties, because we have only the
vaguest knowledge of the extent to which habitually
nocturnal animals rely upon their eyes in obtaining
their food.

162 ANIMAL LIFE IN DESERTS

The difficulty of accepting the view that pale sandy-
tints " protect " the nocturnal animals of deserts, is
as nothing compared with the difficulty of accepting
the same view with regard to certain subterranean
forms. The Pocket-Gophers (Thomomys) of the
southern United States are found in a variety of
environments, including the deserts. They very
rarely come above ground, but none the less those
that live below the surface of the desert are paler
than the others ; the palest of all is Thomomys
alhatus described by Grinnell from the Imperial
region of California. This form is actually the
palest of all the animals of its native region ; and
all the mammals of the Imperial region, which
is desert but not of an extreme sort, are very
pale. It is interesting to learn that the soil in
which this Pocket-Gopher burrows is by no means
very dry.

The Marsupial Mole (Notoryctes), which is a purely
subterranean inhabitant of sandy places in Central
Australia, is pale sandy, frequently almost white, in
colour. It is even more rarely exposed to dayhght
and to enemies on the surface of the soil than the
Pocket-Gopher, and unless we postulate that both
are descended from ancestors which Hved on the
surface of deserts and there acquired a " protective
coloration," we cannot in any way accoiuit for their
colour : for such an hypothesis there is not a shadow
of evidence.

Similar examples occur among the Reptilia. The
Sand Boa {Eryx jaculus) and the nearly Kmbless
Skink {Eumeces scutatus) are animals which live

THE COLOURS OF DESERT ANIMALS 163

nearly all their lives underground : they are certainly
paler and less distinctly marked when they Hve
in the soil of deserts than when they live in the soil
of wooded country, as my friend Capt. C. M.
Ingoldby informs me.

It is generally true that bats of desert areas are
paler above and below than their relations living in
areas which are not desert. Many examples might
be chosen from Persia, Mesopotamia, Egypt, and the
American deserts to show that this diiference is the
rule. This very general truth hardly admits of an
explanation as an example of "protective colora-
tion," for predaceous enemies of bats must be rare ;
and in any case they do not pursue the bat against
a background of desert soil. The most likely
enemies are owls, but in the Great Palaearctic Desert
owls are on the whole not common, except the Little
Owl (Athene noctua subspp.), which hunts in the dusk
rather than at night and is not a serious enemy of
the bats. From what enemy, then, are the bats
" protected," and if a predaceous enemy exists does
their protection not He rather in their speed and
agility than in their colour ?

I have endeavoured to show that the theory of
protective coloration breaks down when we consider
particular animals with reference to their prey or
their predatory enemies. There are other instances
in which the animal's colour should apparently give
perfect protection were it not that its habits are
unsuitable.

One must realize that colour assimilating perfectly
to the natural environment will give little protection

164 ANIMAL LIFE IN DESERTS

unless the animal remains stiU. Abel Chapman has
gone so far as to state it as an axiom that " absolute
immobility, on the part of the object itself, is
essential ; to put it in other words that the slightest
movement, even of a part, is fatal to the value of
any protective principle." I think few of us would
agree to so extreme a statement, but every field
naturaUst knows that it is movement which catches
the eye more readily than colour, or pattern or even
symmetry. The Cream Coloured Courser {Cursorius
gallicus) is as perfect an example as one could find of a
bird which is invisible in desert, so long as it is still ;
sometimes it crouches and then it defies detection
in stony desert at 20 yards. More often it does not
crouch when you approach it, but gets on its long
legs and runs rapidly away ; it stands high above
the ground, casting a conspicuous black shadow in
the bright sunlight, and trusts to its legs and not
to its colour to ensure its safety. Even when it is
not disturbed the Courser is very conspicuous when
feeding in the early morning and late evening : as the
sun is low it casts a particularly large shadow, so
that at these times the bird is easy to see. The same
may be said of many other desert birds which are
beautifully "protected" if you see them in a
museum, but are quite conspicuous in nature
because they do not keep stiU. Most of the larks
of the Great Palaearctic Desert (Ammomanes, Gale-
rida and others) are rather fooHsh Httle birds which
scratch and feed and chirrup within 20 yards of you,
and you can only feel that a Httle ordinary intelligence
would render them invisible. Hey's Partridge {Am-

THE COLOURS OF DESERT ANIMALS 165

moperdix heyi) and the See See (A. griseogularis)
are two small Partridges with exquisite soft buff and
greyish sandy feathers. All through the middle of
the day they lie up in holes in rocks and under
boulders : at the time they are, of course, invisible
owing to their position, not their colour. When the
sun is low they come out to feed ; though their legs
are short their shadow is long at this time of day,
and they are quite conspicuous.

In certain grasshoppers it seems probable that
the coloration is actually protective. Vosseler men-
tions the Short-horned Grasshoppers Eremobia,
Eremocharis, Pamphagus and others, in all of which
the thorax and abdomen are widened and flattened
in such a way that the animal is triangular in
transverse section and flat below. When it presses
its ventral surface to the ground there is no shadow
to betray it, and while at rest it carries the broad
flat femora pressed against the abdomen, thus
contributing to the same result. In this attitude
every visible part of the insect is "desert colour,"
and is roughened so that it resembles rough rock or
sand : bright colours occur on the hind-wings, on
the inner face of the femora, and on intersegmental
membranes, but they cannot be seen while the
insect is at rest. It seems, then, that in these
grasshoppers shape, colour, surface sculpturing and
habit co-operate to render the insect difficult to
see, and one must admit that in these cases the colour
is protective, for it is unreasonable to argue that the
shape, sculpturing and habit are protective, and
that the colour with which they co-operate is due to

166 ANIMAL LIFE IN DESERTS

some other cause. Such cases as this are rare, and
I maintain that the theory of protective coloration
does not cover more than a few of the phenomena.
For instance, among the invertebrata one may find
examples of colour which would conceal an animal
were its habits not faulty. The hovering flies and
bees and wasps to which reference has already
been made (page 148) are a case in point ; so are
many grasshoppers which climb on a stone and
rub their legs together to make a noise, thereby
betraying their position by their noise and move-
ment.

I think, then, that we are justified in saying that
many creatures whose colours would afford them
complete protection if they kept still are rendered
easy to see because their movements annul this
protection : if the colour has a " protective func-
tion," then the habit has an " advertising func-
tion " : a theory of advertisement might be launched,
and could be almost as well supported as the more
popular theory of protection.

And then how many colours there are which we
must frankly say are unsuitable, unless we discard
the theory of protective coloration. I have dealt
at some length with the black forms earUer in this
chapter : let us now consider them from the point
of view of theory. Enthusiastic supporters of
" protective coloration " have realized that a black
and white Wheatear perched on a rock might raise
doubts as to the soundness of that theory, and they
have urged that these birds are not really conspicu-
ous in a bright sun, among dazzling high Hghts and

THE COLOURS OF DESERT ANIMALS 167

black shadows, so long as they remain still ; un-
fortunately Wheatears are active, restless birds and
do not remain still for long. If we grant, what no
one who knows these birds in their haunts will
deny, that they are very easily seen, we may sup-
pose that they are protected from diurnal birds of
prey by their extreme wariness. This might aboUsh
the need for protective coloration, but does not in
the least explain the assumption of black, or black
and white colour.

Remember, also, that the black, or black and
white Wheatears exist side by side with buff and
isabeUine congeners, and the nearly black race of
Calliptamus ccelesyriensis, so far as we know, never
replaces the normal buff typical race of its own
species. The buff and black exist side by side and
appear to fill identical places in the general economy
of nature.

It is this recurrence of blackness, in widely
separated groups of animals, which is so remark-
able. If we may postulate that the Raven has
no predaceous enemies, that Eugaster (page 153)
is protected by its oily secretion from whatever
enemies it has, and that the Wheatears evade the
hawk by quickness and watchfulness, then we can
understand that desert-colour is not necessary to
these animals. But at once we are faced with their
imanimous choice of black : if they are freed from
the necessity of being buff, why are none of them
green, or red, or blue ? We must remember that
black absorbs more radiant heat than any other
colour. Presumably therefore a black creature must

168 ANIMAL LIFE IN DESERTS

evaporate more water than a similar buff creature,
if it is to keep its body temperature below a certain
figure on a particular day. This, one would sup-
pose, would severely handicap the black creatures
under circumstances in which water is extremely
scarce.

And then, again, why in particular do Eugaster
and CalUptamus coelesyriensis and the Wheatears
become black, for it is against their family tradi-
tions ? The Raven and Tenebrionids and the
Scarab, we may suppose, are black because the
colour is ancestral and they found no reason to
alter it ; but the Eugaster and CalUptamus and
Wheatears have broken with aU tradition, and at
present we cannot explain their blackness.

I maintain, then, that protective coloration cannot
be accepted as a theory to explain the very remark-
able coloration of desert animals. It is not easy
to apply it to animals which hunt or are hunted
at night ; or to animals which appear to be without
any large enemies more powerful than themselves, or
to animals whose paUid colour extends to their beUies
and the soles of their feet. It cannot be appHed at aU
to subterranean animals, nor to black animals, nor to
those whose colour would protect them if their
habits were radically altered. I do not deny that
protection is afforded by colour, under certain cir-
cumstances, to certain animals : on the contrary I
readily admit that many desert animals are rendered
invisible by their colour, which harmonizes per-
fectly with their particular environment : most of
these animals are invertebrates and not rapid in

THE COLOURS OF DESERT ANIMALS 169

their movements : to these forms the theory of
protective coloration may rightly be applied. The
point upon which I wish to insist is that the theory
only covers a small portion of the facts ; we must
look for some other cause, and suppose that after
the prevalent buff or sandy colours had become
estabhshed, certain of the creatures used them as
a protection from their enemies : this is equivalent
to saying that the protection afforded is quite a
secondary matter and in no way causal.

If we are compelled to disavow our faith in pro-
tective coloration as the cause of this remarkable
general depigmentation, to what are we to turn for
an explanation ? The cause is one which affects
animals of every type, in every desert ; it does not
discriminate between prey and captor, between the
creeping and flying animals, between the diurnal,
the nocturnal, and the subterranean. It is so
universal in its appHcation that it is probably
physical. No biological agency, such as the struggle
with rivals for food or water, the avoiding of enemies,
or seeking a mate, can cover so wide a range of
animals ; heat alone it is not, for heat in other
parts of the world does not produce these uniform
pale forms ; low or fluctuating relative humidity
it can hardly be, for the animals which live below
stones and in burrows by day, and emerge at night,
are not exposed either to very low or very fluctu-
ating humidity. I am unable to suggest any con-
dition, or combination of conditions, which can
make itseK felt so widely, but I feel that the
explanation will eventually be found in studying

170 ANIMAL LIFE IN DESERTS

the effects of physical conditions upon the animal
life, and that no progress is possible until we rid
ourselves of our belief in protective coloration, at
any rate so far as it is appUed generally to desert
animals.

INDEX

Aciwjia, 137

Acanthodactylus, 118, 130

AdaliinsB, 151

Addax Antelope, 89

Addra Gazelle, 89

Aden, Arabia, 20

Adesmia, 151-153

Adesmiinae, 161

Africa, S.W., 4

Agama, 92, 98

Agriophyllum, 128

Akidinse, 151

Alaemon, 87, 144

Alectoris (Caccabis), 49, 144

Algiers, Africa, 32

AUactaga, 76, 79, 80

Amara, Mesopotamia, 13

America, desert reptiles of, 92, 99

America, N., deserts of, 3, 103, 115,

161
America, S., deserts of, 4
Ammi, 124

Ammomanes, 87, 111, 112, 144, 164
Ammospermophilus, 89
Amphibolunis, 143
Amu Darya, Turkestan, 51
Amydrus, 49
Anderson, 126

Anderson and De Winton, 117
Andijan, Turkestan, 13
Animals, coloration of, 140-170
Animals and drought, 81-92, 127
Animals and heat, 98-108
Annual plants, 57-58, 123-125
Antechinomys, 78-80
Anthia, 130

Ants in deserts, 71-72, 83, 103
Ants, honey-pot, 72, 120
Ants, sand-dwelling, 119-120
Ant-chat, 112

Apterous insects in deserts, 113
Apus, 94-95
Apus {see Cypselus)
Arabia, 49-50
ArctiidsB, 114
Arctotnys, 134

Artemia, 95

Asphodel, 59, 126

Astacopsis, 96

Athene, 104, 163

Atkinson, 81

Atriplex, 45, 64, 100, 127

Augidras, 21, 28, 43, 88

Australian deserts, 6, 12, 73, 92, 95,

96, 98, 100, 101, 104, 116, 137,

142, 143, 161
Available moisture, 14

Babylon, Mesopotamia, 16

Bagdad, California, 11

Baghdad, Mesopotamia, 7, 12, 17,

19
Bahrein, Persian Gulf, 7, 20
Bairam Ali, Turkestan, 13
Balud Ruz, Mesopotamia, 30
Bannerman, D., 145
Base -levelling, 66
Basra, Mesopotamia, 12, 13
Bateson, W., 134
Batin, Arabia, 50
Bats, 83, 87, 104
Beaucamea, 61
Bees, 67
Belenois, 69
Beni Ounif, Algeria, 12
Birds' eggs, 105-107
Biskra, Algeria, 72, 73, 129, 155
Blaps, 104, 150, 152
BlaptinsB, 151

Blatter, E. and Hallberg, F., 40, 48
Bombyliidse, 148, 149, 162
Boreida, Arabia, 43
Brine-Shrimp, 95
Bubo, 104, 160
Bucanetes {see Erythrospiza)
Bulbul, White-cheeked, 74
Bullfinch, Trumpeter, 86, 111
Bunting, Striated, 86
Burrowing animals, 102
Bustard, 87, 145
Butterflies, Blue, 110
Butterflies in Mesopotamia, 67

171

172

INDEX

Caccabis {see Alectoris)

Cactus family, 60-63, 128, 135, 138

Cactus, Giant, 62, 131, 132, 135

Cahuilla, California, 31

Calexio, California, 9

Callegonium, 110

Calliptamus, 153, 167

Callisaurus, 118

Calotropis procera, 61

Camel, 88, 99, 137

Camp, C. L., 117, 166, 169

Camponotus, 72

Cana, F. R., 43

Canary Islands, 145

Cannon, W. A., 31, 136

Caper bush, 68

Capparis, 68

Caprimulgus, 141, 149

Carabidse, 104, 113

Caracal, 160

Caspian Sea, 62

Caterpillars and wind, 114

Caves, 48, 49, 104, 105

Centunis, 132

Ceramodactylus, 118

Cerastes, 130

Cercomela, 112

Cereus, 62, 131, 132, 135

Chaman, Baluchistan, 7, 18

Chapman, Abel, 89, 112, 164

Charadrius, 108

Chilades, 68, 111

Chiroleptes, 97, 98

Chlamydotis, 87, 145

Chough Thrushes, 87

Chuckwalla, 98

Cinnyris, 134

atellus, 89, 115

atruUus, 55, 135, 138

aay Desert, 37, 44

Clay, desert, saltness of, 45, 46

Closed basins, 51

Colchicum, 59

Coleoptera, wingless, 113

Colias, 67

Colocyiith, 55, 138

Coloration of animals, 140-170

Columba livia, 105

Coney, 49

Coniliunis, 77-80

ConiontinsB, 151

Corvus, 49

Courser, Cream-coloured, 86, 107,

140, 157, 164
Cricetulus, 146
Crickets, 66, 103, 113
Crocus, 59, 126
Cro talus, 159
CryptochilinsB, 151

Ctenomys, 116

Cursorius, 86, 107, 140, 157, 164

Cypselus, 104

Date Palm, 42, 135
Date Palm, fauna of, 102
Dead Sea, Palestine, 46, 52
Death Valley, America, 52
Dera Ismail Khan, India, 8
Desert, Great PalsBarctic {see Great

Palsearctic Desert)
Desert Quail, 87
Desert soils, 36-50
Desert Warbler, 83
Deserts, definition of, 2
Deserts, extent of, 3
Deserts, temperature of, 16-22
Deserts, watercourses in, 49-51
Dew, 14, 81
Didelphys azarce, 156
Dipodillus, 77, 79, 103, 127, 161
Dipodomys, 79, 103
Dipodops, 103
Dipus, 75-80
Doughty, C, 43, 88
Dragon-fly, 94

Drought, effect on mammals, 73
Ducrosia, 124

Dunes, sand and rainwater, 41
Dust -devil, 29
Dust-Mulch, 39

Echinocactus, 62, 135

Echinops, 128

Eggs of desert birds, 105-107

Egypt, 126

Eland, 89

El Arish, Sinai, 20

Eleodinse, 151

El Paso, Texas, 12

El Wed, Algeria, 32, 42

Emberiza, 86

Ephydridse, 94

Eremiaphila, 99

Eremobia, 165

Eremocharis, 165

Eremophila, 111, 140, 144

Erodinse, 151

Erythrospiza, 86, 111

Eryx, 162

Estheria, 94

Eublepharis, 92

Eugaster, 153, 155, 167, 168

Eumeces, 162

Euphorbiaceae, 60

Euphrates, River, 50, 51

Eurychorinse, 151

INDEX

173

Evans, W. E., 65
Evaporation, 30-33

Falco (Falcon), 133, 162, 168, 169

Fennec Fox, 116

Fischeria, 99

Floods, 50, 96

Flycatcher, 133

Foeniculum, 124

Forbes, R., 10

Fort Mohave, Arizona, 9

Fossors, 67

Fox, 116, 127, 146, 158

Francolinus, 87

Fresh -water fauna, 93-98

Frogs, Australian, 95-98

Galerida, 86, 130, 143, 144, 164

Oalerida cristatay first plumage, 145

OalicUs barbara, 156

Gazelle (Gazella), 89, 99

Oeococcyx califomianus, 147

GeometridsB, 141

Gerbil, 77-80,102, 138, 146, 160, 161

Gerbillus, 77, 79, 80

Ghardaia, 17, 18, 31, 32, 143

Giant Cactus (see Cactus)

Giraffe, 89

Gizeh, Egypt, 24

Goats eating Zizyphus, 138

Gobi Desert, China, 20

Golodnaia Steppe, Turkestan, 13

Gopher, 162

Graphipterus, 130

Grasshoppers, Long -horned, 113,153

Grasshoppers, Short-homed, 99,
113, 153, 165

Gravel desert, 48

Grazing animals, 136

Great Palsearctic Desert, 3, 6, 41,
47, 59, 89, 100-104, 110, 123,
135, 138, 150, 152, 154, 163

Great Salt Lake, Utah, 52

Gregory, J. W., 88

Grinnell, J., 115, 131, 132, 147, 162

Ground Squirrel, 89, 116

Gryllidse, 103

H
Hamster, 146
Hare, 99, 127, 144, 146
Hare, Cape Jumping, 78
Harrison, L., 98
Hart, E. C, 126, 138
Hartert, E., 10, 42, 72, 111, 129,

143, 165
Haywood, A. H. W., 10, 88
Hedin, S., 44

Heleioporus, 97

Heliotropium, 110

Helwan, Egypt, 16

Hemiechinus, 83

Hermetia, 92

Hibernation in desert insects, 71

Hingston, G. W. G., 92

Honey -pot Ants, 72, 120

Hornet, 87

Himiidity, 22-27

Humus, scarcity of, 36, 41

Hyla, 96

Hymenoptera, 66, 87, 125, 148

Hypocolius ampelinus, 136

Hyrax, 49

Imperata, 110

Indian Desert, 7, 8

Indio, California, 11

Ingoldby, C. M., 92, 163

In Salah, Sahara, 19

Insect eaters, rarity of, 79, 83

Insectivora, 83

Insects, seasonal abundance of, 65-

73
Ipomsea, 61
Iris, 59, 126
Isidorella, 95

Jackals, 135, 138, 158

Jacobabad, India, 18

Jaculus, 75, 76, 79, 80, 90, 103, 161

Jaffa, Palestine, 42

Jaisalmer, India, 8

Japyx, 101

Jaxartes, River, 51, 52

Jerboa, 74, 82, 102, 160, 161

Jericho, Palestine, 57

Jodhpur, India, 13

Jordan Valley, Palestine, 6, 46, 52

K
Kangaroo Rat, 115
Karachi, India, 8
KasaUnsk, Turkestan, 17
Kidal, Sahara, 10
Kit Fox, 116
Kobelt, 134
Kufara, Libya, 10

Laghwat, Algeria, 31, 32, 143

Lake Eyre, Australia, 52

Lanius, 100

Larinus, 129

Larks {see Alsemon, Ammomanes,

Galerida, Rhamphocorys)
Lasiocampidse, 114

174

INDEX

Lava, fauna of, 145-146

Lepus, 127, 144

Libyan Desert, 11, 33, 48, 109

Light, 33

Limnodynastes, 96

Liparidae, 114

Livingston, B. E., 39

Lizards, Sand-dwelling, 117-119

Loess, 41, 44, 46

Lophortyx, 87

Loranthus, 134

Lucas and Frost, 142

Luxor, Egypt, 22

Lycium, 125

Lymantriidse, 114

M
MacDougal, D. T., 4, 55, 56, 61
Mandali, Mesopotamia, 86
Mantis Family, 66, 99, 113
Marmot, 134

Meade-Waldo, E. G. B., 84, 107
Meinertzhagen, R., 144
Melophorus, 72
Menjil, Persia, 28
Meriones, 77, 79, 92, 130, 146, 161
Merlin, 158
Merriam, C. H., 156
Mesopotamia, 46, 65, 70, 71, 90, 92,

102, 103, 124, 127, 135
Micropallas, 132
Mohammerah, Persia, 25, 26
Mqhave, Arizona, 12, 31, 32
Mdle, Marsupial, 162
Mole-rat, 126

Mollusca in Australian deserts, 95
Moloch, 92
MolurinsB, 151
Montgomery, Punjab, 8
Morice, F. D., 148
Mosquitoes, 94
Mosul, Mesopotamia, 17, 26
Mouse, House, 102
Mouse, Spiny, 102
Multan, India, 8
Mus, 78, 102
Myiarchus, 133
Mjrmecobius, 83
Myrmecocystus, 72
Mzabite cemeteries, 136

N
Nefud, Arabia, 43
Nemestrir^idsB, 148, 149
Nesokia buxtoni, 103
Nettles mark camp sites, 134
Newt, 93

Nightjar, 141, 149, 150
Nile, River, 61, 108

Normand, C. W. B., 29
Notomys, 77, 79, 80
Notoryctes, 83, 116, 162
Nukus, Turkestan, 18

Oasis, 54, 55, 74
Ochotona, 147
(Edicnemus, 86
CEnanthe {see Saxicola)
Onion, 59

Oodnadatta, Australia, 12
Opuntia, 136, 138
Oran, Algeria, 32
Omithogallum, 59
Orthoptera, 66, 112
Oryx Antelope, 89
Ostrich, 89, 105, 106
Otus, 133

Owl, Eagle, 104, 160
Owl, Elf, 132
Owl, Little, 104, 163
Owl, Screech, 133
Oxus, River, 51, 52

Palaearctic Desert {see Great False -

arctic Desert)
Palestine, 20, 42, 47, 102, 103, 114,

126, 128, 148, 151, 153
Parnphagus, 165
Panicum, 110
Papilio, 124
Pamara, 68
Partridge {see under Alectoris, Am-

moperdix, Francolinus)
Passer, 100
Paulsen, O., 19, 41
Pedetes, 78-80
Peile, H. D., 124
Perognathus, 79, 80
Peromyscus, 146
Persia, 161

Petroalexandrovsk,Turkestan, 1 7, 20
Phascogale, 73, 78-80, 125
Philby, H. St. J., 50
Phoenix, 135
Phrynocephalus, 118
Phyllopoda, 94
Pieris, 67

Pigeon, Rock, 49, 105
Punelia, 151, 152
PimeUinsB, 151
Pistacia, 137
Pitman, R. B., 103
Piute Dam, Utah, 31
Plover, Kitlitz, 108
Pocock, R. L, 117
Podoces, 87
Poecilocerus, 154

INDEX

176

Polygonum, 110

Porcupine, 49

Port Said, Egypt, 7

Praocinse, 151

Pratincole, 105, 107

Predaceous animals, 168-160

Prezhevalsky, 20

Prickly Pear, 136, 138

Procavia, 49

Proctor, J., 119

Prosopis, 125

Protective coloration, 146, 148

Protaetia, 129

Protozoa of sand, 121

Pterocles, 84, 144, 146, 157

Pulicaria, 110

Pycnonotus, 74, 100

Quail, Desert, 87

Raczkowski, 46

Rain, effects of abundant, 72, 74

Rainfall, 6-14

Rainstorms, 13, 60

Rajputana, India, 48

Rattlesnake, 159 —

Raven, 164, 167, 168

Rhamphocorys, 111

Roadrunner, 147

Rock Desert, 48

Rock Doves, 49, 105

Rodents in S. Palestine, 126

Roebum, Australia, 12

Rohlfs, 19

Rothschild, W. (Lord), 111

Ruby Wasps (Chrysids), 67

Ruta, 124

S
Sahara, 19, 32, 42, 43, 47, 72, 111,

112, 129, 137, 143, 145, 165
St. George, Utah, 9
Salsola, 55, 127, 129
Salton Sea, Arizona, 12, 62
Salts found in deserts, 46, 46
Sand desert, 40
Sand desert, fauna of, 116-121
Sand-dwelling Protozoa, 121
Sandgrouse, 84, 105-107, 128, 146,

169
Sauromalus, 98

Saxicola, 49, 100, 112, 130, 154, 155
Scaptira, 118
Scarab, 162, 168
Scarturus, 76, 80
Schimper, 136
ScincidflB, 117
Seeds, spiny and hooked, 135

Semi-deserts, definition of, 2

SepidinsB, 151

Shakespear, 50

Shamal, 27

Shrike, Great Grey, 100

Silt, 44

Silvery insects in deserts, 148

Sirocco, 27

Sminthopsis crasaicaudata, 73

Soil, relationships with, 114-121

Soil, temperature of, 20-22

Soils, water capacity of, 37-39, 44

Spalax, 126

Spalding, V., 135

Sparrow, House, 100

Spencer, B., 73, 74, 95, 101, 126,

137, 143
Spurge Family, 60
Squill, 69, 126
Squirrel, Ground, 89, 115
Star of Bethlehem, 59
Stenodactylus, 118, 130
Stone and earth desert, 47
Stone Curlew, 86
Stones, animals living imder, 100-

102
Storey, G., 152
Su8Bda, 45, 66, 127
Succulence, 60-62
Sudan, 17, 112
Sumner, F. B., 141, 146
Sunbu-d, 134

Swallow-tail Butterfly, 124
Swifts, 104
Sylvia, 83

Syr Daria, Turkestan, 61
Syrrhaptes, 128

Tabanidas, 94, 148

Tachta, Turkestan, 19

Takla Makan, China, 43

Tanezruft, Sahara, 88

Tarucus, 67, 111

Tashkent, Turkestan, 7, 17, 20

Taterona, 77

Telphusa, 95

Temperature, daily range of, 19

Temperature, extremes of, 17

Temperature, monthly average, 16

TenebrionidsB, 104, 113, 130, 150-

153, 166, 168
TentyriinsB, 151
Teracolus, 68, 69
Teratoscincus, 118
Terebinth, 137
Thomas, H. H., 48, 109
Thomas, O., 160
Thomomys, 162
Thomson and Thomson, 121

176

INDEX

Thominess, 62, 136-139
Ticehurst, C. B., 74, 86, 106
Tidikelt, Sahara, 10
Tigris, River, 60, 61, 65
Tiliqua, 100

Toes, reduction of, 74-76, 80
Traganum, 10
Transcaspia, 46, 50, 52
Treefrog, 96
Tripoli, Africa, 19
Tristram, H.B., 126
Tristram's Grackle, 49
Tucson, Arizona, 9, 12, 22, 31
Tulip, 59
Tuomey, 131, 135
Turkestan, 46

Urginea, 126
Uromastix, 155
Utah, America, 52

Vegetation, annual, 57-58, 123-125
Vegetation, perennial, 68-62, 125-

133
Vespa, 87
Volga, River, 62
Vortex, 29
Vosseler, 165
Vulpes {see Fox)

Wadi Dawasir, Arabia, 50

Wadi Haifa, Egypt, 16, 17

Wadi Hanifa, Arabia, 50

Wadi Rummah, Arabia, 49, 50

Wadi Solaf, Sinai, 50

Warbler, Desert, 83

Wargla, Algeria, 12, 19

Wasps, 67

Watercourses, 49

Water Melon, 138

Water Supplies, 81

Wheatears (Saxicola = (Enanthe),

49, 167, 168
Wheeler, W. M., 71, 120
Wild boar, 126
WiUiams, C. B., 21, 22, 104
Wind, 27-30, 108
Wind, affecting bird life, 111-112
Woodpecker, 132

Yuma, Arizona, 12, 31

Zamenis, 130

Zapus, 76, 79, 80

Zarafshan, River, 55

Zizera, 67

Zizyphus, 55, 100, 111, 125, 137

Zophosinse, 161

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AUTUMN

ANNOUNCEMENTS, 1924

♦■•■»

THE YEARS OF MY PILGRIMAGE.

By the Right Hon. Sir JOHN ROSS, Bart., last Lord Chan-
cellor of Ireland.

One Volume. Demy Svo. With Portrait. 18s. net.

Sir John Ross, the distinguished Irish judge, has hved through
an eventful period of history, during which he has met many of
those who played a memorable part in public affairs. The judicial
system which was carried on within the walls of the Fom* Courts in
Dublin vanished with the destruction of that beautiful and noble
building in 1922, and it seemed fitting that some one should essay
a portrayal of the personalities and surroundings of a Bench and
Bar so famous in their day, and inter alia rescue from obUvion
scenes and stories of their times. This Sir John has done with the
happiest results, and there are few of the well-known men of his
day who do not figure in his pages. But the book is by no means
confined to legal luminaries or to striking incidents in Civil and
Criminal Trials. The author sat as a Member of Parliament for
years, and though he eschews politics as such, he has many good
stories of election times and of life in the House. The leaders of
Irish Society, both men and women, were well known to him, and he

2 Edward Arnold dh Co.*s Autumn Announcements,

draws interesting pictures of Court ceremonial and social functions
in pre-war days. Nor is sport forgotten, nor the humorous side of
Irish life, which suggests a fund of entertaining anecdotes and stories.
It is interesting to know that though Sir John, an Ulsterman, lived
in Southern Ireland for more than forty years and in the execution
of his duty was often obHged to do unpopular things, he can write
that " neither I nor any member of my family had to complain of
an unkind deed, or even word.'*

LIFE OF JOHN WILLIAM STRUTT,
THIRD BARON RAYLEIGH, O.M.

Sometime President of the Royal Society and Chancellor of
the University of Cambridge.

By his Son, ROBERT JOHN STRUTT, FOURTH BARON
RAYLEIGH, F.R.S.

Late Fellow op Trinity College, Cambridgb.

One Volume. Demy Svo. With Portraits. 25s. net.

In writing this book, Lord Rayleigh's aim has been not so much
to give an account of his father's scientific work as to depict him
as a man. The narrative would, however, be without substance
if his scientific career was not made its guiding thread. In the
selection of topics, it was clearly impossible to refer to more than a
small fraction of the papers in the six large volumes of his col-
lected writings. The topics have been chosen for their comparative
simplicity and for their bearing on the external circumstances of
his life. Many investigations of epoch-making importance have
necessarily been left unnoticed. But it is hoped that some others
have been brought within the reach of readers who would be
repelled by the severely technical form of the original accoimt.

Lord Rayleigh's friends included the most eminent men of his
day in the spheres that appealed to him : among those who figure
in these pages are Dr. Routh, Charles Darwin, Clerk Maxwell, Mr.
Gladstone, Lord Salisbury, Lord BaKour, Lord Kelvin, Mrs. Sidg-|
wick, Joseph Chamberlain, Sir J. J. Thomson, Sir J. Larmor andj
many others. In his later years Lord Rayleigh amused himself b]
making a collection of humorous stories and anecdotes, and though]
some of them may be famifiar, it has been thought worth whilt
reprinting the collection in an Appendix,

Edward Arnold <fe Co.' 8 Autumn Announcements. 3

MEMORIES OF A MILITANT.

By ANNIE KENNEY.

One Volume. Demy 8vo. With Illustrations. 16s. net.

The reader will not get far into this volume without falling in
love with Miss Annie Kenney, however strongly opposed he may
have been to the Suffragette campaign. The fight is over and the
angry passions roused by it have subsided, so that in a calmer
atmosphere we can admire the courage, resourcefulness, and devotion
to their cause of women who Uke Miss Kenney were ready to sacrifice
everything for a principle. She and her friends possessed the
qualities of which martyrs are made, and though we may laugh
at the humours of the struggle, actual tragedy was never far off.
Fearsome and terrible indeed to the feminine nature must have been
the hostile crowds, the certain prospect of rough handling, of arrest,
prosecution, imprisonment, and forcible feeding. The protagonists
were no viragoes, but well-educated women from happy and com-
fortable homes, to whom the mere thought of making themselves
conspicuous would in ordinary Hfe have been abhorrent. Miss
Kenney herself is evidently one of the kindhest folk, though her
zeal knew no bounds. Probably she seemed to her opponents a
dangerous fanatic, but she reveals herself in this book a true woman,
tender-hearted, sympathetic, cheerful, and gaily humorous whatever
happens. Her devotion to the other leaders of the Movement was
unbounded, and it is interesting to read her affectionate tribute to
ladies whose very names were anathema to the other side during the
heat of the fray. Interesting too are the interviews she reports
with statesmen of the day — Sir H. CampbeU- Banner man, Mr.
Lloyd George, Lord Balfour, and Mr. Asquith — ^whose methods of
dealing with very perplexing and novel situations differed widely.

HUIA ONSLOW.

A Memoir by MURIEL ONSLOW.

One Volume. Demy ^vo. With Portraits. Price 12s. 6d. net.

Victor Alexander Herbert Huia Onslow, younger son of the 4th
Earl of Onslow, was born on November 13th, 1890, in Government
House, Wellington, New Zealand, where his father was then Gov-
ernor . To commemorate the place of his birth he was given the Maori
name of Huia, by which he was known throughout his hfe. He
was educated at Eton and Trinity College, Cambridge. At the
University he studied Natural Science and, later. Mechanical
Science, his intention being to qualify for the Parhamentary Bar,
but during a mountaineering holiday in the Tyrol, he met with an

4 Edward Arnold dh Co.'s Autumn Announcements.

accident, while bathing, which left him paralysed below the waist,
with no hope of recovery.

It was in these circumstances that he determined to devote what
time and energy remained to him to the cause of Science, and for the
rest of his life he worked with indomitable courage and brilhant
success at intricate biological and biochemical problems, taking
special interest in Mendehan research. The success was the more
astonishing inasmuch as many of his investigations called for
exceptional manual skill, which he acquired by dint of almost
incredible perseverance, in spite of the fact that his hands and arms
were still partially paralysed. In the summer of 1921 a list of his
pubhshed scientific works was submitted to the Council of the Royal
Society, in order that he might stand for election as a Fellow, but
he died before attaining that distinction, on June 27th, 1922, leaving
an example of high courage to which it would be hard to find a
parallel.

FROM CHINA TO HKAMTI LONG.

By Captain F. KINGDON WARD, F.R.G.S.

Author of " The Romance of Plant Hunting," " The Mystery Rivers

OF Tibet," etc.

One Volume. DemySvo. With Illustrations and Map. 18s.net.

Captain Kingdon Ward has already made a reputation as one of
the most intrepid explorers of the difficult and little-known country
on the marches of Burma, China, and Tibet. The important journey
described in this volume gives the reader an insight into the changes
— physical, climatic, and botanical — which take place as the traveller
passes westwards from the Yangtze across that narrow strip of
earth's crust where the great rivers of South-East Asia escape from
Tibet, and where jungle hides the head- waters of the mighty Irra-
waddy. Captain Ward's primary object was to discover new plants,
but to reach the wild districts which are his hunting-ground is no
light task. Even to reach the city of Likiang in the heart of Asia
involves a formidable journey, for there is no " Magic Carpet " to
transport one thither. A glance at the Map which accompanies
the book shows how formidable were the obstacles he had after-
wards to surmount, at one moment bathed in tropical heat in the
river valleys, at another wellnigh frozen on mountain ridges, 16,000
feet above sea-level. Of great interest, apart from the difficulties
of travel, are his accounts of the inhabitants and their manners and
customs. Captain Ward possesses striking descriptive gifts and
an admirable style ; he has the philosophy of a man who has spent
much of his life in the vast open spaces of the world ; above all, he
has the spirit of adventure.

Edward Arnold dh Co.'s Autumn Announcements. 5

RUSSIA AND RUSSIAN ART.

By SIR W. MARTIN CONWAY, M.P.

FORMEBLY SlADB PrOFESSOR OP FiNE ArTS IN THE UNIVERSITY OF CAM-
BRIDGE. Author op " Palestine and Morocco," etc.

One volume. Demy Svo. Illustrated. 16s. net.

The present condition of Art in Russia has received little attention
since the war, and Sir Martin Conway's visit this summer cannot
fail to throw much new light upon an extremely interesting subject.
Magnificent collections of pictures and priceless objects of Art
formerly existed in Petrograd and Moscow, but how far they have
suffered destruction or dispersal during the last few years is an open
question. The result of Sir Martin Conway's inquiries will be
extremely valuable to all students and lovers of Art in this country,
and his shrewd and impartial observations on the general state of
the country in 1924 will be especially welcome in view of the too
often one-sided and interested glimpses which reach us from the
interior of that darkened land.

ADVENTURES OF CARL RYDELL.

THE AUTOBIOGRAPHY OF A SEAFARING MAN.

Edited by ELMER GREEN.

One Volume. Demy Svo. With Illustrations and Map. 18s.net.

This is a thrilling tale of adventure by a sailor of the old school,
in various parts of the world. Carl Rydell is a Swede who began
his remarkable career in the Swedish Navy. But being of an unruly
disposition he soon got into trouble with the authorities, worked his
way out to America and had a chequered career for many years,
finally coming to anchor as Superintendent of the Nautical School
in the Philippine Islands. *' I am not proud of some of my doings,"
he says, " but I have told the bad along with the good " ; and as few
men can have seen more of the seamy side of a sailor's life, his narra-
tive is extraordinarily interesting. In 1888 Rydell found himself in
San Francisco, and it was on the Pacific coast that most of the follow-
ing years were spent. That was the exciting period of the gold rush
to Alaska, the period of sea-otter hunting and fur-seal " piracy,"
when bold men defied the law at the risk of their lives and were
ready to suffer incredible hardships in their lust for gold. Many
curious characters, the flotsam and jetsam of civilization, figure in
these pages, and the whole book is one of those rare human docu-
ments which a seafaring life occasionally creates for the enjoyment
of the stay-at-home reader.

6 Edward Arnold d; Co.'s Autumn Announcements.

JORROCKS'S JAUNTS AND JOLLITIES.

BEING THE HUNTING, SHOOTING. RACING, DRIVING,
SAILING, EATING, ECCENTRIC AND EXTRAVAGANT
EXPLOITS OF THAT RENOWNED SPORTING CITIZEN,
MR. JOHN JORROCKS OF ST. BOTOLPH LANE AND
GREAT CORAM STREET.

By R. S. SURTEES,

Author op "Handlhy Cross," "Mr. Sponge's Sporting Tour," btc.

With 15 Coloured Plates after H. Aiken. Crown 4:to.
21s.net.

Robert Smith Surtees, the greatest hunting novelist of all time,
whose biography has just been published sixty years after his death,
has only recently begun to receive his due from the Uterary critics.
Yet he is the man whose gift Thackeray once said he envied more
than that of any man. And no wonder he did — for Surtees is the
Dickens of the hunting field, and many of his odd characters are more
ahve to-day than most of our flesh -and-blood acquaintances. Sur-
tees is a national treasure, for he is one of the most peculiarly English
writers of the last century. His pages are crowded with delight-
fully drawn types, and of them all none is more beloved than the
immortal John Jorrocks. It was the success of '* Jorrocks's Jaunts
and Jollities," according to Mr. Thomas Seccombe in the Dictionary
of National Biography, which led to the conception of a similar
scheme which resulted in '* The Pickwick Papers."

'* Tobe taken before * Handley Cross ' " is the author's recommen-
dation in his preface to the second edition of this jolly book, in
which are recorded the " eccentric and extravagant " exploits of
Surtees' greatest character. And those people who have not
already made the famous grocer-sportsman's acquaintance will do
well to follow it and read of the earlier doings of the M.F.H. of
Handley Cross. Those who are already devotees of this delectable
story-teller will need no recommendation, beyond the fact that they
have here for a reasonable price a handsome reproduction, including
Aiken's famous coloured plates, of a work which in its earlier editions
costs from fifty to a hundred pounds, according to the state of the
copy purchased.

Edward Arnold d; Co.'s Autumn Announcements. 7

UNSCIENTIFIC ESSAYS.

By F. WOOD JONES, M.B., D.Sc.

Elder Professob op Anatomy in the University of Adelaide. AtrrHOR
OP " Arboreal Man," etc.

One Volume. Crown Svo. 6s. net.
Professor Wood Jones is one of those men whose scientific attain-
ments are combined with the possession of a charming Hterary
style, and who, like Huxley, Drummond, and Fabre, have the art
of writing round science in a way that the pubUc can understand and
enjoy. The pages of this volume are the products of his idle
moments, some of them passed in London, some in Austraha, and
some upon a Coral Island in the Indian Ocean. The short essays
have fascinating titles. Who would not envy the author his
acquaintance with Fire-flies, with the Sea Serpent, with Wer
Tigers ? The first chapter on *' Marvels " strikes the keynote of
much that follows. Such essays as those on Evil Spirits, Moon-
gazing, the Crab's Secret, Oily Patches, Sights and Scents, show how
varied and uncommon is the menu presented to us. In others, less
intriguing headings such as Coco-nuts, Seals and Sea Birds, Coral
Islands and Clay Pans serve as pegs on which to hang a wealth of
original thought and suggestion. And all through the book runs
a strong vein of sentiment and romance which adds to the subtle
spell the author weaves for our enchantment.

ANTIQUES :

THEIR RESTORATION AND PRESERVATION.
By A. LUCAS, F.I.C.,

Chemist in the Department of Antiquities, Cairo.
Crown Svo, 6s. net.
The preservation of antiquities is one of the most difficult problems
that confronts collectors and curators of Museums and Art Galleries.
Mr. Lucas has written a practical account, devoid of technicahties,
so that his accumulated knowledge may be readily available to
those interested in the subject. His practical experience has
extended over a number of years, and he has recently been
associated with Mr. Howard Carter in regard to the preservation
of the numerous art treasures found in the Tomb of Tutankamen.
He commences with a general account of methods of preservation
and restoration, emphasizing the necessity of a prehminary
examination as to the nature and composition of the object before
applying any specific treatment. This is followed by an account
of the best methods available for use with the different materials
such as papyrus, paintings, bronzes, etc. — ^the materials being

8 Edward Arnold <fh Co.^s Autumn Announcements,

arranged in alphabetical order. Finally, descriptions are given of
certain simple physical and chemical tests which should be applied
to the object in order to obtain information as to its composition,
with a view to ascertaining the best method of preserving it.
Detailed instructions are given for making up any solutions required
in the course of the work.

A HUNDRED YEARS IN THE HIGHLANDS.

By OSGOOD MACKENZIE.
New and Cheaper Edition. Crown 8fo. Illustrated.
7s. 6d. net.
The late Mr. Osgood Mackenzie's delightful collection of Highland
lore and memories, including those of his uncle. Dr. John Macken-
zie, has passed through several editions in its original form, and has
been acclaimed as worthy to rank with such classics as Scrope, St.
John, and Colquhoun. This new and cheaper edition will undoubt-
edly be warmly welcomed by a large circle of readers for whom the
price of the original work was somewhat high and will enable the
possessor of the smallest library to add to it a work of the highest
interest. *' To all those," said The Times, " who reverence ancient
customs and lore of the West Coast Highlands, this book will be
a real dehght." The Author loves the hills and the sea, the heather
and the loch. He loves the people, their language and traditions ;
he has even a soft place in his heart for their superstitions. All
forms of Highland sport are familiar to him, and he possesses a keen
and kindly sense of humour, which gives rise to many a well-told
anecdote and permeates the whole book.

ENGLISH LITERATURE BEFORE
CHAUCER.

By P. G. THOMAS, M.A.,

Reader in English Language and Literature in thb Untstbrsitt

OF London.

One Volume, Demy %vo. 8s. 6d. net.

The time has gone by in which it was possible to speak of Chaucer
as " the Father of English poetry." He will always remain one
of its greatest masters, but investigation into the sources of English
literature has brought to light materials many centuries older, and
these not merely of antiquarian interest, but evidently the pro-
ducts of an advanced civilization.

In this book the author has set himself the task of giving within
moderate compass and without excessive detail a reasoned serial
recital of the examples we possess of Old and Middle English

Edward Arnold d; Co.^s Autumn Announcements. 9

literature, and an illuminating exposition of their value and char-
acteristics, both linguistic and literary, thus bringing into clear
perspective the development of the various forms which served
as the prototypes for later work.

Not only will the book prove a useful introduction to the student
preparatory to a more detailed study of individual texts, but the
reader whose literary interests are more general, and to whom this
period has been perhaps a terra incognita, will find much to attract him
in the early examples of EngUsh epic poetry, romance, lyric, satire,
and the short story, with whose later manifestations he is familiar.

TRAGEDY.

By W. MACNEILE DIXON, LL.B., Litt.D.

Professob of English Language and Literature in the University

OF Glasgow.

Crown Svo. Probable price, 6s, net.

Though the author of this Essay points out some features of the
Athenian theatre which fatefuUy combined to favour the birth
of Tragedy, he is not greatly concerned with any ordinary question
of " origins," and holds simply that Tragedy burst from the brain
of ^schylus like Athena from the head of Zeus, attaining at once
its fullest imaginable stature. The justification of " the ways
of God to Man," "the Problem of Evil," "the Riddle of the
Universe " — in such phrases as these Professor Dixon's concep-
tion of the scope of the Tragic theme are faintly adumbrated,
and one is left wondering whether, without ^Eschylus' lead, even
Sophocles would have compassed it fully ; of Euripides there is
no question. Only once — with Shakespeare — was Tragedy reborn.

The history of Tragedy is thus not a literary one ; it is to be
sought rather in a way in which the world-philosophers, from Aris-
totle to Hegel and Nietsche, have reacted to it. In the tracing of these
reactions lies perhaps the principal interest of a stimulating book.

NEW FICTION.
MUCH DELUSION.

By GERTRUDE SPINNY,

Author of " The Painted Castle."

Crown Svo. 7s. 6d.

Miss Spinny's first novel, " The Painted Castle," won golden

opinions from discerning critics who were quick to recognize qualities

revealing unusual promise. In her new novel, the author has

chosen a less difficult subject and one that will appeal more directly

10 Edward Arnold dh Co.'s Autumn Announcements.

to the experience of the reader. The story is Hghtly and amusingly
told while developing a situation that becomes increasingly excit-
ing. It begins quietly with the appearance of a stranger, Andrew
Redman, who takes a furnished cottage in Sussex to recover from
a nervous breakdown. He becomes acquainted with his neighbours,
in particular with the Vicar, who is morbidly interested in Spiritual-
ism, and with Miss Charlotte Masters, who Hves there with her grand-
parents. Charlotte is regarded by the Vicar as a promising medium,
and by Redman with eyes of love. Gradually the reader perceives
that Redman is living under an assumed name, and learns that his
breakdown was caused by circumstances not unconnected with the
Vicar's mental disturbance. Redman's identity, when revealed,
adds to the difficulty of his winning Charlotte. But a more terrible
obstacle arises through the menacing attitude of the Vicar, whose
delusions rapidly develop into mania and bring about a catastrophe
in which Charlotte barely escapes a horrible death. The story is
■carefully constructed and interesting from start to finish.

THE PAPER MOON.

By L. C. HOBART,

^ Author op " The Silken Scarp."

Crown 8vo. 7s. 6d. net.

Miss Hobart's second novel is in every way stronger and more in-
teresting than her first. The plot is weU constructed and developed
with much emotional power. She has the gift of bringing her charac-
ters and their setting vividly before the reader, and communicates
the strong sympathy and antipathy she herself feels for them.

The book opens amid idyllic surroundings on Dartmoor, but the
scene soon shifts to a certain house in Chelsea, in outward appear-
ance not different from its neighbours, but pregnant with some
strange uncanny influence, some dimly apprehended evil lurking
in the background, waiting for the moment of consummation.
This malign atmosphere, the tense expectancy, the breathless
suspense, Miss Hobart renders most vividly.

The inhabitants of the house are Jonathan Fane and his son
Greville ; from them also there seems to emanate a mysterious sug-
gestion of hidden evil, of menace that may become reality. Greville
is the villain of the story : he is a man who exercises irresistible
iascination over the opposite sex, and first April Arless, then Rachel
Strangways fall victims to his Mephistophelean attractions. In strong
contrast with Greville is his cousin, Jake Fane, who is also in love
with Rachel, and the characters of these two men typify the forces
of good and evil which contend for mastery throughout the book.

Edward Arnold <fc Co.'s Autumn Announcements. 11

THE BIRTHMARK.

By ALAN SULLIVAN.
Crown 8vo. 7s. 6d. net.

Mr. Sullivan's book is a sheer delight. Conceived in a spirit of
satiric comedy, it is packed with witticisms that keep the reader
chuckling happily to himself from the first page to the last.

To Molding-on-the-Ooze, in " the lowest, flattest and dampest
section of the Midlands," the seat of Henry Hardinger, Esq., come
Colonel and Mrs. Bostwick, desiring its owner as a husband for
their daughter Grace. Henry (who looks on life " as something
between a polo match and a satiric comedy ") has no money 'f the
Colonel has no money : each is ignorant of the other's want : each
sees in Grace a solution of his difficulty. Every one takes a hand
in the game of deceits, and as all concerned are both deceivers and
deceived, the complications and the fun can be imagined.

Mr. Sullivan is never at a loss : he *' keeps the ball rolling '*
merrily. Unhesitatingly he puts his finger on the laughter-feedmg
qualities in every one and every thing. He mocks, but it is with a
kindly mockery that adds zest to life.

As for the Birthmark — the part it plays in the game it would be
unfair to reveal, but the comedy both above and below stairs makes
joyous reading. To all who enjoy laughter we recommend this
whimsical and witty book.

SMITE THE ROCK.

By OSWALD H. DAVIS,

Author op " Soft Goods."
Crown 8vo. 7s. 6d. net.

All readers of Mr. Davis's brilUant first novel must have looked
forward with eager interest to a second book from his pen. They
will not be disappointed.

" Smite the Rock " is, like " Soft Goods," a chronicle of the
great Midland city of Ardencester, and is marked by the same
sincerity and fineness of detail that distinguished the earher book.
Life in a provincial city : the niceties of its class distinctions : its
" high teas " : its chapel '* socials " : the ughness of its industrial-
ism, are described with a vividness that is almost imcanny.

Against these pettinesses of existence : these social differentia-
tions : the drabness of the workers' hves : the things that " always
have been and always will be," Frank Calder rebelled. The son
of an employer and a capitalist, he ranges himself on the side of

12 Edward Arnold db Co.'s Autumn Announcements.

Labour, only to find his idealism shaken by contact with the indi-
vidual representatives of the class he champions, and by the brute
force of the mass. But the ideal of service, the purity of his con-
ception, the instinct to fight for an idea, survive, and the book
ends on a note of high hopefulness.

Mr. Davis's subject is a fascinating one — ^the gradual development
of a young man's character, his aspirations, his temptations — and
he has handled it with masterly skill.

A QUEST FOR A FORTUNE.

" By PHILIPPA TYLER.

Crown Sw. 7s. 6d. net.

The scene of this interesting story is laid in Italy, land of romance
and intrigue, which has so often attracted English novehsts and pro-
vided them with exciting and entertaining plots. It was the happy
hunting ground of Marion Crawford and of Richard Bagot, to mention
only two favourite authors, and after reading Miss Tyler's work
one wonders whether there is not some special deity who smiles
upon the choice of that wonderful land as a field for fiction. Miss
Tyler's novel has the atmosphere of Italy breathing through every
page. We have the old aristocracy typified in the Prince di Consa
and his beautiful daughters : like their magnificent palaces, glorious
without, but faded and decaying within, the family presents to the
world an appearance of stateliness and pride of race which hide
ruined fortunes and an abandoned morale. The Prince himself
carries off the situation boldly to the end, but the inevitable crash
develops and wellnigh overwhelms his son Sigismondo, round whose
efforts to restore the family fortunes the plot thickens. A good
marriage is evidently the obvious solution, but what shall a young
man do when love pulls one way and purse-strings another, not to
speak of a very able and intriguing Marchesa di Pina who knows
exactly what she wants and holds strong cards played with entire
unscrupulousness. The Marchesa is a most original and effectively
drawn character, and both Anita and Raffaella are such charming
girls that it is hard to say which is the real heroine. We have pur-
posely avoided unravelling the plot, which is extremely ingenious and
well constructed and holds the reader's attention to the end.

THE MIND OF MARK.

By H. HERMAN CHILTON.
Crovm 8vo. 7s. 6d. net.
This is Mr. Chilton's first novel, and it is made noteworthy by
his clever study of the character of his hero, Mark Rawson. The

Edward Arnold d; Co.'s Autumn Announcements. 13

author knows intimately the manners and conversation of the self-
made Midland manufacturer and his associates, and his picture of
Mark Rawson, so utterly absorbed in " getting on " — in " besting
the other chaps " — that his home is, as it were, but a bye-product,
has a photographic exactitude.

As Mark's wealth had increased, so had his self-confidence and
dominance. Once resolved on a course of action, he bends his
Board of Directors to his will. When a strike occurs, he thinks
to dominate his workpeople in like manner. But they are of less
pliant material, and in the uproar Mark receives an injury to his
head which brings on a long illness.

For the first time in his life, he becomes an onlooker : he has
leisure to think, and begins to readjust his values, to see that
there is such a thing as compromise.

But this new Mark Rawson is incomprehensible to his colleagues
and — with the exception of his daughter Amy — to his family :
he loses the support of the one and the sympathy of the other.

The sincerity and power of the book are unmistakable, and the
tragedy of the end is marked by a fine simplicity.

A PASSAGE TO INDIA.

By E. M. FORSTER,

Author or " Howabds End," etc.
7s. 6d. net.

*^* Also a Collector's Large Paper Edition, limited to 200 copies,

each copy signed by the Author, printed on Hand-made paper.

Demy 8vo, price £2 25. net.

Reviewed by Rose Macaulay in The Daily News : " Mr. E. M. Forster
is to many people the most attractive and the most exquisite of contemporary
novelists. . . . Never was a more convincing, a more pathetic, or a more
amusing picture drawn of the Ruling Race in India. . . .

"It is an ironic tragedy, but also a brilliant comedy of manners, and a
delightful entertainment. Its passages of humour or beauty might, quoted,
fill several columns."

Reviewed by Sylvia Lynd in " Time and Tide " ; *' Reader, lo here, at
last, a great book. There have been brilliant books in recent years, witty
books, original books, books written in limpid and exquisite English ; but
not imtil now has there been a book that was all these things. . . .

" ' A Passage to India ' is a delicious and terrible book. ..."

From The Spectator : " Of all the novels that have appeared in England
this year, Mr. Forster's is probably the most considerable. . . .

" ' A Passage to India ' is a disturbing, uncomfortable book. Its surface
is so delicately and finely wrought that it pricks us at a thousand points.
. . . The humour, irony, and satire that awake the attention and dehght
the mind on every page all leave their sting."

14 Edward Arnold d; Co.'s Autumn Announcements.

Uniform Edition of

Mr. E. M. Forster's Earlier Works.

A new uniform edition can now be obtained of the following books.
Bound in cloth, bs. net per volume.

A ROOM WITH A VIEW.

*• Mr. Forster's new novel clearly admits him to the limited class of writers
who stand above and apart from the manufactm*ers of contemporary fiction."
— Spectator.

*' It is packed with wonderful impressions and radiant sayings." — Evening
Standard.

" We have originality and observation, and a book as clever as the other
books that Mr. Forster has written already." — Times.

THE LONGEST JOURNEY.

" This novel is a very remarkable and distinguished piece of work. Its
abundant cleverness fills even the more strenuous passages with vivacity.
The strength of the book consists in its implicit indictment of the mean,
conventional, self-deceitful insincerity of so much of modern EngHsh edu-
cated middle-class life. This is certainly one of the cleverest and most
original books that have appeared from a new writer since George Meredith
first took the literary critics into his confidence." — Daily Telegraph.

WHERE ANGELS FEAR TO TREAD.

*' A remarkable book. Not often has the reviewer to welcome ''^a new
writer and a new novel so directly conveying the impression of power and
an easy mastery of material. Here there are quaUties of style and thought
which awaken a sense of satisfaction and delight ; a taste in the selection
of words ; a keen insight into the humour (and not merely the humours)
of life ; and a challenge to its accepted courses. It is told with a deftness,
a lightness, a grace of touch, and a radiant atmosphere of humour which
mark a strength and capacity giving large promise for the future." — Daily
News.

HOWARDS END.

Crown 8vo. 6s. net. A few copies still obtainable.

" There is no doubt about it whatever. Mr. E. M. Forster is^one of the
great novelists. All will agree as to the value of the book, as to'its absorb-
ing interest, the art and power with which it is put together, and they will
feel with us that it is a book quite out of the common by a writer who is
one of our assets, and is likely to be one of our glories." — Daily JTelegraph.

Edward Arnold d; Co.'s Autumn Announcements. 15

RECENTLY PUBLISHED.

MAN AND MYSTERY IN ASIA.

By FERDINAND OSSENDOWSKI,

Offiohsb d'Aoad6mie FiiANgAisE ; Authob of " Beasts, Men and Gods.'*

With Map. Demy Svo. Third Impression. 14s. net.

Morning Post. — " Every whit as enthralling as ' Beasts, Men and Gods.' '*

Spectator. — " The most salient feature of Dr. Ossendowski's book is its

revelation of the author's complex character. We are deeply impressed by

his power of telling a story, for every chapter is not only interesting, it is

exciting. One of the most exciting and vivid narratives we have ever read.'*

THE ROMANCE OF PLANT HUNTING.

By Captain F. KINGDON WARD,

Author of " The Land of the Blue Poppy," etc.

With Illustrations and Map. Demy Svo. 12s. 6d. net.

Mr. Horace Hutchinson in The Queen. — " It is a book to be much com-
mended to the expert and to the general reader alike."

THE LAND OF THE SUN (QUEENSLAND).

By E. J. BRADY,

Author of '* Australia Unlimited," " The King's Caravan," etc.
With Illustrations and Map. Crovm Svo. 7s. 6d. net.

Liverpool Courier. — " Reads like a novel and sounds like a poem."

LIFE AND ADVENTURE IN PEACE AND

WAR.

By Majoe-General Sir ELLIOTT WOOD, K.C.B.
One Volume. With Portrait. Demy Svo. 16s. net.

THE ASSAULT ON MOUNT EVEREST.

By Brig.-General the Hon. C. G. BRUCE,
And other Members of the Mount Everest Expedition.

With 33 Full-page Illustrations and 2 Maps. Med. Svo.

25s. net.

16 Edward Arnold dh Co.'s Autumn Announcements.

RECENTLY PUBLISHED.

THE WANING OF THE MIDDLE AGES:

A STUDY OF THE FORMS OF LIFE, THOUGHT AND ART

IN FRANCE AND THE NETHERLANDS IN THE I4TH

AND 15TH CENTURIES.

By J. HUIZINGA,

Pbofessok in the Univeesity of Leiden.
With Illustrations. Demy Svo. 16s. net.

" This thoughtful and well-ordered book, full of strange facts and shrewd
comment, deserves careful study. The illustrations are delightful, and have
evidently been selected with great care and judgment." — Times Literary
Supplement.

THE DISINHERITED FAMILY:

A PLEA FOR FAMILY ENDOWMENT.
By ELEANOR F. RATHBONE, M.A., J.R, CO.,

Author of " How the CAsuAii Laboureb Lives," etc.

Croum Svo. 7s. 6d. net.

Sir Wm. Beveridge in the Weekly Westminster. — " A remarkable book
compact of vigorous argument and marshalled facts and wide personal ex-
perience. It can be read by anybody and ought to be read by everybody."

SUNSHINE AND OPEN AIR :

THEIR INFLUENCE ON HEALTH. WITH SPECIAL
REFERENCE TO THE ALPINE CLIMATE.

By LEONARD HILL, M.B., F.R.S.,

Director Department of Applied Physiology, National Institute of
Medical Research.

Illustrated. Demy Svo. 10s. 6d. net.

This book is well worth reading, and although of particular interest to
the medical profession, should be much more widely appreciated. Both medi-
cal and lay readers will find it full of interesting facts and permeated through-
out with shrewd common sense." — The Lancet.

CRIME AND INSANITY.

By W. C. SULLIVAN, M.D.,

Medical Superintendent State Criminal Lunatic Asylum, Broadmoor.
One Volume. Demy Svo. 12s. 6d. net.

" We can thoroughly recommend this book to both jurists and medical
men." — British Medical Journal.

London : Edward Arnold & Co., 41 & 43 Maddox Street, W.l

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